1. See page 20 of the launch press kit: https://www.jpl.nasa.gov/news/press_kits/mars_2020/download/...
Sure, for stuff you can reasonably test in Earth gravity and atmosphere you can just weld stuff together in a field and then fly it until it stops crashing. Thats a case when you can iterate quickly and relatively easily with lots of COTS stuff.
For comparison: SpaceX's entire Falcon 1 program cost $90M over 6 years. That was to develop two new rocket engines (Merlin & Kestrel), build out the launch site on Omelek Island, and launch five times.
As to the SpaceX point. Yes, I think SpaceX is more efficient with their money than NASA, but this will boil down to a discussion of counterfactuals and degrees of "wastefulness". Was NASA wasteful? What does it mean to be wasteful? What's the threshold? What would it cost SpaceX to build the Mars Helicopter? Can we really compare a launch vehicle versus a tech demo of a rotorcraft operating on another planet? Would that $80M be better spent just funding SpaceX? I don't know. I just don't think it's fair to simply say "If it was made with off-the-shelf parts then it's a testament to how wasteful NASA has become". The engineering has to happen. Could NASA have been more efficient with it? Probably. Was it wasteful? I don't think so.