Putting down a new floor (especially when you have access from below) is not technically hard. It is a lot of work.

I'd consult a book or two to make sure I haven't glossed over some of the important points, but off the top of my head, here's the order:
- remove fixtures (and plug the toilet flange)
- cut back to solid flooring (next to a joist is good)
- match thickness of existing flooring (and don't get fooled by a sample of swollen wood). It ought to be 5/8 or 3/4.
- put blocking flush with the joists at every seam
- while you're at it, cross-brace or block your joists for a more solid floor for the tile
- cut and dryfit the new floor (plywood recommended). Make sure your toilet flange is still the right height.
- put a bead of construction adhesive on every joist/block
- place the new floor and screw it down on 8" spacing everywhere there's something to screw into.
- screw your old floor down too, if there's any of it left
- put down vinyl. (Knowing that it's temporary, I'd use double-sided carpet tape around the perimeter. I'm sure that makes me a hack.)
- replace fixtures. Don't try this at a time when the plumbing supply store is closed. Inevitably, something has crumbled and needs to be replaced, or you forgot to buy a new wax ring earlier. Turn water on and hope for an absence of leaks.
- drink a beverage of choice and pat yourself on the back for a job well done.

Nigel's subfloor instructions are good. Here are my answers to your additional questions.

I've only laid vinyl once, and torn it out twice, but in all 3 cases on top of the subfloor, which remains through any type of flooring, there was an ~1/8" underlayment of luaun, screwed down every 8" or so. The vinyl is then glued to to the underlayment.

Ripping it out entails a wonderbar, hammer, and a little elbow grease. Ok, a lot, as you have to pry out all the screws too. But you could tear out a bathroom your size in an hour or two.

Tile requires a different underlayment: cement board or (WAY better) Ditra (google it if you don't know what it is). So you've got to tear out the vinyl with its underlayment (you're not going to separate them anyway), add new underlayment, and tile over that.

Putting down a new subfloor and underlayment is a DIY job. As the others suggested, get a home repair manual to get a better idea of the other posts instructions. The manual is a good investment. Enjoy learning and working on this new project...you can do it.

Casey

"http://www.driverdb.com/Sean McDonagh"

Thanks everyone. I've requested some diy flooring books from the library to better gauge whether or not this is something I can tackle.

If we decide to get outside help, where would I begin finding someone? And how much should I expect to pay?

Thanks again!

Flooring books may or may not help... try also the general purpose home books (the Big Orange Box has one called "Home Improvement 1-2-3", for example. It isn't very good for the subfloor part of this task, but has okay information about the plumbing and finish floor side of things.) If you don't already own one like this, I'd suggest you get one for everything else you might want to do around the house.

There's no perfect category of trade for this job. Part of the complication is that plumbing usually requires a license, so you'd be taking a bit of a chance to have an unlicensed individual working on the plumbing.

If you go to a plumbing company, they might have carpenters that they use, but it'll cost a little more for the coordination they have to do.

If you approach a general contractor, they'll have the carpenter and connections to plumbers, but they might also view this as a small job and upcharge you for the bother.

A handyman without a license to do plumbing would probably do an okay job, but there's a possibility that they'd botch it.

If it was me, I'd try and find a combination licensed plumber/ handyman. You'll pay a little more for the plumbing ticket, but it may help you sleep better at night.

My gut tells me that this would come in under $2000, but there are too many unknowns to even call that a guess. (And double that if you live somewhere really expensive, like California or NYC.) Get a couple of people out for a quote. Ask for proof of liability insurance and call their insurance company to see that they're currently covered.

To drag you back to the DIY side of things, if you feel competent and safe with a circular saw and a drill, and own basic plumbing stuff, then I think you can do this. Double that vote of confidence if you have another bathroom in the house to use while this one's being wrecked.

Thanks justnigel. I've requested the "Home Improvement 1-2-3", as well as a couple of other general home improvement books ("How Your House Works" visual guide seemed like a good choice).

We live in Utah, but $2000.00 still seems like an awful lot of money so we'll probably give DIY a try! And we do have another bathroom we can use while this is in progress (thank goodness!)

I'm not really sure though where the plumbing specialists come into this? I understand we will need to temporarily remove the toilet and sink, but other than turning off the water and plugging the flange, is there something I'm missing? We hadn't planned on moving or changing the fixtures.

I didn't mean to scare you about the license stuff... it's just one of the many things to be aware of when getting trades into your home. In general, if you have an unlicensed individual do work that should have been done by a licensed person, then their screw-ups become your problem.

In your case, the plumbing specialist mainly comes into play if something goes wrong. Removing and replacing fixtures isn't hard.

One more bit of advice, if I may: check beforehand if your toilet and sink have shutoff valves. If they don't, then your first task is to put shutoffs there, so you can get water to the rest of the house while you're working on this room. The compression fit ones work quite well.

And I might be completely wrong about the $2000. Not a bad idea to get at least one quote. (On the other hand, I'm sure the DIY will be very satisfying.)