Basically, all you do is get the cheap $10 or so air compressor and remove the case. Some attach battery clamps so they can attach the cord directly to the battery. I found a very small compressor and removing the case did not reduce the size very much so I left it on and store it in the space that the CD player should reside. I added a power outlet and have it attached directly to a fused power plate so that amperage is not an issue.
I would take a guess that if you opened up that $80 models aluminum project box, you would find the same guts as the $10 or $15 ones you find at WalMart. I was pretty lucky, I already had one of those small compressors, and its plastic case wasn't oversized, so I didn't even need to remove the case!
Or you can always make your own, buy the cheap air compressor, go to Radio Shack and buy one of their aluminum project boxes, take off the plastic and put the rest inside the project box. VOILA! :lol: