This is a 2ft by 4ft back-lit sign, made to look like the Portal video game. (You probably already gathered that.)
The entire project came in under $200 for me. The biggest cost is going to be your sheet of glass or plastic for the front. I used white glass from a local stained glass shop. 2ft x 4ft was the largest size it came in. If I was going to do this again, I might try to use a white plexiglass or plastic, but I think that was actually more expensive at the time.
Even lighting is probably going to be the most difficult thing to achieve. In the photographs the sign looks very evenly lit, it is less so in real life. (Some of the other pictures show this better. I used two off the shelf light fixtures that had circular fluorescent tube lights. I might look for something different if I were to try again. Maybe this? ("2-D shaped" light bulb.)
One final note: I'm going to talk you through my process for making my light. If you want to make your own there are several dependency routes which you can follow. By this I mean: If you choose your size first, that will determine the panel material, which may determine the lights you can use. If you choose your lights first, that may dictate the size of the sign and therefore what panel materials will work. Finally, if you choose panel material first, that will determine your size and probably your available lights as well.
Okay, on to the materials. I'll list the main ones here quickly and go into more detail on the next pages.
2 ft bx 4 ft sheet of white glass ~ $60
Clear Adhesive Film ~ $10
(I used Grafix Ink Jet Adhesive Film from Amazon.)
Adhesive backed Black Vinyl ~ $10
(Again, from Amazon I got Cricut Vinyl)
Fluorescent Light Fixture of some sort.
I used a GE circular fluorescent light fixture from Menards.
1x4 boards, of various lengths (2x 4ft, 5x ~2ft)
Wall plug and cord
Aluminium foil or other reflective material
Total Cost: ~$200, if you don't have to buy the tools.