Here's what you need and about what it'll cost you:
A big box, the squarer, the better (Free)
A piece of poster board ($1 at Dollar Tree)
White muslin fabric to cover the holes (I already had this but you can buy $2 a yard cheap stuff from JoAnn's)
Two lamps (Standing lamp was $5.99 and clip on lamp above was $9.99 at Target)
Daylight bulbs - 60 watts ($5 for a pack of 4)
Box cutter, tape, scissors
Buy your lamps before getting your bulbs so you can check the maximum wattage your lamps can handle. I bought 100 watt bulbs before finding that the only lamp that could support that bulb would cost $30.
Follow the tutorial here to put it all together!
Here's the first photo I took without any adjustment:
And after a little adjustment in iPhoto to brighten it up:
Not perfect, but it'll get there. I might take the photos into CameraRAW or Photoshop to lighten up the shadows more. But overall, it's a success!