Okay, so I've been reading this and comparing prices on parts and what not.
Seems like parts kits are still reasonably priced. 150 or so at Apex.
Receivers are milled, so they aren't a BIY item. Must come through an FFL, and they are the expensive part, $400 and up.
Finished rifles are in the $800-$900 range. I think though that if you build a rifle because you think its cheaper than buying you'll quickly find you aren't saving any money.
Jacques, any chance your son will make more of the clamps to sell? And, we need pics of the finished product or the write up is incomplete....
If you had some extra time on your hands, you could probably polish the gas piston to look like the original.