Hobby Lobby had a couple sizes last year when I was looking.
I want to say they were around $30 and $60. They aren't very big.

Hazie

I want a light box too but plan to have DH construct it. It looks simple enough to do. One of these gals here has a homemade one--it MIGHT be CALAM.

I have a big one hubby made me this time last year.
{{!gwi}}

It looks a little different now. I frosted the glass, and put a shelf on the bottom.

Hazie

I also have a home made one. Not as nice as hazies though.
The top is about 3x4' and the legs are made of 4x4 posts! (This thing is heavy as a BIG dawg) I have a 1/4" piece of glass inset so it's flush on the top, then there is a 4 bulb florescent fixture hangin underneath it by chains. It has that diffuser thingy on top of it. When I'm not using the table as a light box, I have a piece of plywood that goes on top so I can do stones or whatever.

My light box is also homemade. I use the morton cutting grid as my light box top. It works great. Had the hubby make the frame. I think the most expensive part was the light that went inside. I already had the morton cutting grid, I flip it over to the flat side for tracing or looking at glass in the light.

Here's the home made lightbox hubby built for me. I love it! It's on casters so that it rolls wherever I need to use it. He also incorporated some nice storage underneath and I have some stained glass scraps organized in recycled Circle E candle jars. Handy!

(also 4x4 legs! men want everything huge!)

Here is a link that might be useful: lightbox