My thoughts...Buy the 2nd car, and cut your losses. You will spend more money than that on replacement panels, junkyard trips, and materials trying to fix the 83 SS. IF it's a good donor, you will have your frame, and body issues solved. Now for the $700... offer him $400. The car is not worth any more. If he was going to fix it, he would have done so by now, It has been sitting for a few years to be in the dirt like it is. The mirror holes have let water in all that time. He's not capable of fixing it, and he needs Xmas $$$ . IF he balks on the $400, settle at $500, and spend the extra $200 on the wife!