I don’t know about you, but the thing that drives me nuts the most is finding resistors and capacitors of the right value and rating. Before, in solid state circuits, we gave little thought to ratings. In guitar amps you have to observe max voltage ratings and pick components with reasonable voltages. I try to scrounge these parts but the more I do this amp stuff the more I have to go out and buy these components. At least with new parts I can feel better about good performance. As I move away from prototype designs, I will use less recycled parts. If I decide to stabilize a project to duplicate it, I will look for parts that I can get that are acceptable and reasonable cost. In the long run, I think that custom amps will not be built just to save some money on a new amp. But more to get something unique and built to personal taste.