I know it says MUSCLE CARS but this $600 Cadillac was directly responsible for my first GTO. I bought the Caddy for $600 in '80 and swapped it even for my first GTO in '82...So, I guess, the answer is '$600'.
My friends thought I was crazy to give up to uber-clean 80,000 mile Caddy for a beat up looking GTO but I never looked back. In fact, I never did get over my first GTO. Super solid, great original car just needing a little paint and the bumper straightened out. Pic was taken the day I brought it home.