Wow, this saddens me. When I search your local craigslist, I find perfectly working cars, with current registration, good tires and working AC, many for under 2 grand. But she's too attached? This appears to be such a waste of resources during a very trying time. My folks had some help from SBK. I certainly wouldn't have stuck my dad with a project car in his last years. You just watch the money go out the window during that time and wait for the doctors to give you results that always come in months later when you needed to react in days or weeks.
How much did that drive shaft cost? If I worked for SBK I'd be pretty pissed that we just paid for a driveshaft for a sports car that still can't past smog, runs like crap and isn't street legal due to missing headlights. I have a feeling your in for more of that similar work on this car. Mechanics need to be paid for their time. Easily a few grand, just to get it barely working I think. That roof top and bumper and lights will be cosmetic, so that's pretty expensive. I suppose having time and transportation you can go search junk yards for affordable parts. Just to fix what you have here in your first email I'd say is like 4 grand, and that is having her do the wrench turning and part hunting as much as possible. Maybe you can help her get some quotes for the big picture and see where to go from there.
A knock sensor is a serious PITA for these cars. Mechanics charge at least $1000 and the dealership has it listed at $3000. Definitely make sure you have the code in the car before tackling the work. You can try to replace or relocate the sensor, or put in a resistor.
http://twinturbo.net/nissan/300zx/forum ... ation.html
detonation-sensor-t341113.html
I apologize a bit. I want to help. I want to do my best with that. I don't have my dad anymore and it was recent enough to affect my thinking process with this. Honestly, I think the best help is to get her into a different car and sell this one to an enthusiast who doesn't need it for transportation.
https://sandiego.craigslist.org/ssd/cto/5757324934.html
https://sandiego.craigslist.org/esd/cto/5783159013.html