My first build (a Romy which I'm putting the finishing touches on now) cost me somewhere in the $150-$170 range for parts (kit, receiver flat, center pin & sleeve, rivets and screws, and US compliance parts). Unfortunately, the days of $90 Romy kits is gone, and I haven't seen any parts kit group buys in a while, but a home build may still be an economical way to go.
That price doesn't include the parts and tools I'd bought for the project (including a bending jig, rivet removal jig, and shop press) which brought the total cost to quite a bit more. They'll be re-used for a few more kits and then perhaps sold. I was also able to make use of other people's equipment (spot welder, drill press, upper rail template) which kept my costs down.
If you do get a build party going in the near future, I'll be happy to lend my jig and press, and can supply some pointers (although I'm by no means an expert)