This setup could be used for anything from macro photography to online inventory photos. I give the measurements for my version, which is about 18" by 18", but you can scale it up or down however you'd like. The whole shebang can be made for between $20 and $25, depending on if you already have the tools and some of the materials. It also takes only a few hours to make. I actually took about 9 hours to build it originally, but that's because I had to redesign it several times before I was happy with it. This instructable only covers the box itself, the lighting is up to you. I used my two incandescent desk lamps and a vivitar 283 flash, and was quite happy with the results. Also, I know it looks pretty ugly in the photos. I'm not very good with scissors.
Addendum: I apologize for the weird black spots all over a bunch of the photos. I took my D40 camping recently and the sensor got a good bit of dust on it and it is greatly affecting the pictures. I managed to manually clean it about 3/4 of the way through the instructable.
Step 1: Step 1: Materials & Tools
Hacksaw or PVC cutter (not pictured, I got mine cut at the store)
Common office stapler
Exacto knife or utility knife.
Now: Materials and cost
11x 16" lengths of 1/2" PVC pipe: $2.29 for a 10ft section at Ace Hardware, and they'll usually cut it to size in the store
-Note: You could technically get away with using 10 sections, which would make the joints a little bit cheaper, but at the cost of making the frame a lot more flimsy.
2x 90 degree 1/2" PVC joints: $1.29 apiece
6x 1/2" PVC three-sided corner joints(Don't remember the exact name): ~$1.89 apiece
1 24" set of white sticky back velcro: about ~$3 or $4 at Wal-Mart
1 20" x 30" Elmers Foam Board: ~$4 at Wal-Mart, may have been cheaper, I can't remember
1 70" x 71" Frosted Shower Curtain: $2.14 at Wal-Mart