Cost of rusty project or parts car

I pay $650 for 4 door parts cars (up from $500 15 years ago).

If there are "desirable" parts I know I can sell fast or that I need, then I will up my offer if refused, otherwise it's $650 take or leave.

In that past 7 years, the most I've paid is $1200 and that was for a 72 Charger with bucket seats, "clock"/150 rally cluster, hidden headlights, and a 3.23 sure grip 8 3/4.

Last month I offered $200 for a 71 Satellite. No sale but I added up about $400 in sales other than long term and miscellaneous "smalls", plus the labor to strip, storage space and dealing with the carcass. The asking was actually only $400.