I posted pictures from most of the steps on Bandit's blog, it starts at the bottom of the page I linked to.
http://www.rabbitsonline.net/showthread.php?t=73547&page=39 I can't remember how much it cost me, but it was quite a lot. I think I bought 4 boxes of grids at $25 each, the plywood for the floors and the vinyl covering together probably cost me about $60 (at a guess), though I'm sure I've written it down somewhere. Then there's all the odds and ends, like the glue for the vinyl, the 400 odd cable ties, white plastic stripping to secure the edges, the pine edging, screws, clips for the doors, core flute for the wall, and the list goes on.
If your cage is a little smaller you can probably buy 3 boxes of grids instead of 4. You definitely need a floor surface for any upper level but not necessarily for the bottom level (depending on the bunny).
I bought my grids online, since they're not sold in stores in Australia. But in USA you can get them from Bed, Bath and Beyond, Target (watch out for the grids with the larger openings as bunny heads can get stuck, so if you get a box with some of these, use that grids with those holes for the roof or for under the flooring of a top level), and probably more places. All of my other supplies I bought at a home improvement store called Bunnings, which is similar to Home Depot.
My advice to you is to plan the design of your cage. How many grids high/long etc. Work out how many grids you'll need, decide what you're going to use for the flooring and how you're going to put it all together. Work out what tools, if any you'll need for each step, and how much of each material you'll be using. Then you can write up a list and go to the store and cost it up.