Hi Rebecca,
I resurfaced a floor recently and it was more or less in the same condition as yours, which is good and won't take that much work.
I used the second hand held sander down shown here : http://www.wisegeek.com/what-is-a-hardwood-floor-sander.htm#
I used coarse/medium grit (#60) sandpaper to start then finished off with fine grit (#100).
i also used a cushion as it gets pretty hard on the knees.
Keep a hand brush handy to clear the dust and a big damp cloth to wipe over from time to time to check the result.
For the hard to get at edges and corners wrap sandpaper around a small block of wood, sanding in the direction of the wood grain, not against. - (same for the sander BTW)
To even up and slightly deepen the color i wiped over a couple of times with well diluted walnut stain (very cheap stuff ^^) it's always better to take it slowly this way and let it dry to see if you need to go darker.
I then nourished it with a mixture of linseed oil and turps but this can take some time dry and for the odors to dissipate, otherwise there are many other finishing options available on the market, also depending on the kind of wear that your floor will endure.

Small sanders are inexpensive but it's better to invest in one of the heavier models as this will mean less pushing down, therefore less back and shoulder tiring.
Avoid being tempted to rent a big industrial sander as they need some experience, technique and a certain muscle power to control.

Good luck with your project, it's wonderfully satisfying when you can sit back, admire your beautiful floor, having done it all yourself AND saved $$$.

Your floors do look like they are in pretty good shape. If it's one room, I think magada has described a beautiful way to revitalize your floor on your own. My husband and I did an entire house ourselves. He is the one who used the industrial sander and we did fill in some areas with walnut stain with a few coats of polyurethane for a glossy shine. It was quite a job but we were happy to have completed the project ourselves and saved money as we were remodeling the entire home ourselves. Best of luck with the floors whether you choose to do it yourself or hire someone!

I would suggest getting a quote from a professional regardless...and ask for portfolio pics. Magada's description sounds like a lot of hard work to me...I'd want options to consider :)

Get some quotes for refinishing.

Miss Mustard Seed has info on refinishing her floors on her blog. She's on the second go round because there were mistakes made the first time. I had my floors professionally refinished and would never tackle that project myself even though we do most things ourselves.

Err… i think Rebecca may know that she can get a professional quote but (if one reads the OP) would like to do it herself if possible.
This is a comparatively light and easy job, unless like Diana you have an entire house to refinish, and many people aren't afraid of just a little hard work,

My description may seem like much hard work but thats because i detailed a lot.
For 30 m2 (333 ft2) i spent 5/6 hours for each pass, the finishing was fun stuff, i borrowed the sander and the rest cost me about 70€ if that.

Err....magada...for those of us that have done it ourselves and been less than pleased with the results, it's good to knowing going in the extent of the cost...in my case it was much easier, cheaper and faster to write a check than to tackle on my own time. It's not something that's pleasant to drag over several weekends or take vacation from work to complete.

OP is asking for tips and if it can be done inexpensively, which i gave, and which it can.
If she doesn't feel up to doing it herself then she'll probably decide to call in a pro.
OK ?

And I post dilemmas on houzz to get multiple perspectives from people with similar experiences. Or did you want a "you're right, how could I have been so wrong"? Truce.

Thank you for all of your input. I really appreciate Magada breaking everything down for me, it was extremely helpful. You just gave me the motivation I needed to do this project :) I can't wait to get started; I don't mind breaking some sweat. Lol I enjoy doing projects like this and I will enjoy it even more after its done.

@magada...
So in essence, you feel that the ONLY worthwhile "tips" are those that align themselves with your line of thought?
IMHO, the suggestion that someone consider the amount of time, effort, & expense... along with the risk of doing more damage than good IS a "tip".

Protect your air passages/lungs if you are going DIY! Plastic/tape up to protect your family too!

rent a box sander, don't do it with a little hand held one. Box sanders should still be used with the grain of the wood, but you can turn them too without causing issues. I would take off any trim pieces around the floor so you can get as close as possible to the edge, you may still have to use a hand sander on the very edges and in corners. Wherever you rent the sander from can help you get the correct sandpaper sheets. It is a lot of work to clean up the dust- you want to get ALL of it. After sanding sweep or vacuum up as much dust as possible, then wipe the floor down with tack cloth to get any little invisible bits. I always clean my floors with rubbing alcohol before I stain them. I am not a professional, but have refinished wood floors in several of my homes. It is a lot of physical hard work, but it feels good to say you did it yourself.

You're welcome Rebecca, and i hope that you get plenty more encouraging tips and advice here.
Maybe Google around and get as much gen as possible too, and if you have DIY friends they may be able to help point you as well.
And of course, as suggested, protect yourself with a mask and remove all dust before applying any finishes.

@ Select Hardwood
In a word - no.
And don't twist my intentions.

There are several factors to consider prior to starting to refinishing your floor. As stated prior you can do more harm than good. I am not against any DIY'er but educate yourself first. There are companies out there that will give instruction classes on refinishing your floor and will have all the PROPER equipment for rental. Perhaps there is one in your area. Also some of the big box stores have rental departments with all the proper equipment to do the job. Good luck and happy sanding.

@Magada a.k.a. Daffy Duck...

I was by no means "twisting" your intentions... simply asking for clarification.

However, just for the sake of making a point, I suggest that anyone following your advice (&/or the link you provided)... look beyond the nice photos of people playing do it yourselfer for the camera.
Apparently one of them decided to refinish their PINE floors after coming in from the pool or beach, hence the absence of footwear, which I would also recommend.

At any rate... one should actually try to make it to the 3rd paragraph of your "wisegeek instant expert" website... which points out:
"A drum sander is usually a large machine and requires a certain amount of skill and strength to operate correctly. The power of the drum sander also makes it critically important that it be kept moving at all times when in use, as it can cause damage to the wood if left in one spot for an extended period of time."

In all honesty, I find posting the pics of people using handheld vibrating or belt-sanders somewhat misleading at the very minimum.

For what it's worth, I'd never attempt to dissuade any individual from tackling a project on a DIY level.
More power to them... although it's to their benefit to jump in with as much LEGITIMITE information as possible.
And lastly, one should keep in mind that the anticipated "results" may or may not be as well regarded by ALL, depending on the fine line dividing their perception of a good job vs. politeness.

Good luck to the original poster (OP)!

My ex and I did our own sanding on a living room floor some 30 years ago. It turned out quite wavy!

If you have the guts and patience to tackle this yourself, by all means, go for it. After all, it's your floor.

My husband and I also refinished two bedroom floors with the large and heavy belt sander. Like lizzie91001 says, the floor ended up wavy. And yes it too easy to pause while manoeuvering the heavy vibrating beast which does chew up the floor. Lucky for us it was I a corner and there is still some floor left.
Thank you for the idea of using the heavier handheld sander. I have one more bedroom to try this on. The rest of the house was done by a professional, looked good 25 years ago and now needs freshening.