That's what I did. I combed the net for the cheapest Cornelius I could find, somewhere around $30 on ebay. Most of the other parts came from Home Depot and Rex. I think the ending price including canister was around $110 after I put a stupid Clippard NV w/ LPR on the regulator, nowadays I'd put a Fabco on and save even more money for better quality.
The regs are cheap enough at the right places, the adapter is like a dollar at Home Depot, so is the pipe dope. Grab the rest of the parts and build instructions from Rex and you should be able to build the entire setup for less than $130 as long as you don't get ripped on the canister. Hook up a swap out deal w/ a welding supplier for that. Or you can find one of those paintball tanks with the standard CGA-320 threads, but it won't last as long and may or may not be easy for you to get it refilled locally.