People who I know have raised gardens started out with topsoil mixed with compost from the city(free) thats made from any thing they collect in the trashcans for grass cuttings etc. and street cleanup-tree trimmings etc chipped up.
You have to screen it because there is a lot of broken glass in some of it.
They usually start soil prep in the fall.

Mix in compost,manure etc. and let it set all winter then turn it over before planting in the spring.

A lot of them half empty the beds and add the compost each year.Some empty them completely and use that soil for a compost pile for the next year.
They end up having 2 batches of soil going at the same time.
One in the raised beds and the last years in a pile to compost stuff in all year long.
Just keep rotating the piles back and forth adding compostable stuff to the pile of last years soil for next season.
I've read that rabbit manure is really good to add to raised bed soil along with mass quantities of coffee grinds that people get from starbucks or resturaunts.
Others go to horse stables and get manure and straw from them to compost.
Some have been known to drive around on trash day collecting bags of grass and leaves from their kneibors houses.
I think there is a forum for composting and square foot gardening(raised beds would be there too I think).

Interesting....because that is the EXACT combination of stuff I am using: Leafgro + ProMix + Neptune Fish/seaweed. This is the uncomplicated way to do it. It takes no effort or specialized knowledge - you don't have to compost anything or plan or even think about it; you just buy the two bags of stuff and mix it together and then pour Neptune's on it once a week or so. It's very close to square foot gardening. SFG is peat, perlite/vermiculite, compost. Promix is basicaly the first two and Leafgro is the 3rd. SFG is as time-tested an approach as exists, and promix/leafgro does result in productive peppers.

I'm a little fuzzy on whether the Fish/Seaweed can stand as the ONLY fertilizer or if it needs to be combined with something else after transplant. I will probably combine it with TomatoTone, which has more stuff in it.

Leafgro is good stuff. Quite inexpensive, too, I think because it's a university (of Maryland) project - something like $5 per 2 cu. ft. That's cheaper than bags of crap topsoil from HomeDepot. It now comprises around 1/4 of my total garden soil / growing medium, but I intend to get that up to 1/3 or more in the near future. Wait till you run your hands through Leafgro - you will be sold.

You can use all sorts of soils. I usually use compost, not free for me. It's
a lot of work for me to shovel out a 1/2 yard of compost from truck.
Maybe later. I just bought Scott's Garden Soil, 2 cu.ft at $6, mixed in some
agicultural vermiculite. Put in a little bit of Black Cow Composted Cow
Manure and will add Garden-Tone or Tomato-Tone later. In a 4 x 4 raised
bed, I put a lot of my scrapes from my garden in the fall. Kinda like a
small compost pile. Lots of earthworms in there now. I planted 3 tomatoes
in there.