Meggy Jr RGB
I bought and assembled one of these. It's basically what you're after.
You've got your RGB display, and an atmega168 chip (core of the arduino) (could be a 328 chip too.) under the led board, it's got two driver chips and the transistor bank. It works with the arduino software and has two layers of API to interface with the display. This library is very handy.
A whole arduino is good for setting up, programming and prototyping... but seems a bit sloppy for the final product. Maybe I'm just cheap
atmega328's cost like 6 bucks, and you could probably get a bare 8x8 for 30$. the two driver chips for 8.50$ here,
here. It's certainly not as simple, but it cuts your costs in half or so. 50$ instead of 100$. And of course, you'd have to make a board of some nature. Making your own with perf board or copper clad is easy enough, or you could get a board printed at batchpcb, sparkfun's *cheap* board printing service.
You could, maybe, make a board, and get several made... and sell them as a whole or as a kit.
Just thinking out loud.
Should be a fun project. I don't know how much space is back there, but you could even just buy a meggy jr, and connect the display to the board via cable and mount the board a bit further away from the display.
cheers!