Yes, there is a large amount of pocketbook/copycat cars. I dont blame people, building your own stuff is not easy. If you actually add up your time doing R&D and materials it can be more expensive. However, its more fun and you cant complain about the parts not fitting or them not being how you wanted them.
It depends on the car choice also. You can checkbook hotrod a 67-69 camaro easy. Crate motor, trans from a box, pre assembled subframes, prestamped bodies ect. Try to build a 81 cutlass with a 80 buick V6 drawthrough out of a magazine and its not going to happen. Sometimes I wish I would have just went with a SBO. There was a good 67 330 Olds I could have bought instead of the motor i have now. It probably would be faster, cost less, be more sellable, and probably get the same MPG but it just would be the same.
The short list of home built parts on my cutlass are
-Ported iron heads
-Alky injection
-2.5" stainless down pipe
-Entire underhood wiring harness
-Virtually every hose, trans, powersteering, AC, heater ect.
-Electric fan mounting and various assorted parts
-Air filter stuff
-Spoiler spacers to mount a TA spoiler on a cutlass
-More stuff
If you don't build your car, can you really call it yours?