[944 spec perspective]
Lets see, I just bought 4 engine short blocks, and 5 transmissions for $50 each. That seems to be the going price for wheels as well. With the battle ship bumpers we have, if you get punted, you just hook it up to your tow vehicle, and pull the bumper shocks out. I have lots of bumpers I'd give away from parts cars. These parts are not new, and all not all of them are good, but the price is right, if you know where to look. . There is a huge aftermarket/internet support for these old, lovable German cars, and it's very useful. It won't last forever, but it's good so far.
As far as motors, it is important that you build them well, once, and that costs $3,500-$4,000 to do right. As they say, "cry once". Do it right. They are not tolerant of being sloppy, or bad oil, and #2 rod bearing failures result. For perspective, the first motor that I had built (did it right) in 2007, is still racing competively, and burning no oil this year (in the hands of Angil Blazquez). Never any problems, none. This same builder has built 4 more engines for me as I've turned over cars. No motor failures, including multiple enduro seasons, and an 8 hour enduro for me.
I'm sure SE30 is similar. You have to be more creative, internet savvy, and maybe work harder to keep the costs in line, but it is very doable.
National 944 Spec Series Director
FrankenFortyFour in progress...