My number is 60k based on two formulas:
1) Take a solid 20k car, pay 50k to make it perfect, and expect to lose 10k like everybody else.
2) Take a perfect stock car for 50k and add another 50HP at my rate of $200 per extra HP.
Now the usual "Add another 10k if it has a story" with my apologies for the length but here is an example:
"Craftsman Juan Ortiz found a crumpling note in both Cyrillic and Latin characters as he removed the old backseat leather, Juan stopped all work at the shop until a UCLA expert determined it was a help plea from an unhappy Turkish line worker in Bavaria assembling the car. 'Things never fit, the day hours are short, and german words are impossibly long' wrote worker Fikret in this message-in-a-bottle across oceans and time. Juan thought he could use Fikret's unique expertise for classic car restorations and went to Facebook to look for an unhappy Turk in Munich named Fikret. He has not found him but has made 3000 new Facebook friends name Fikret".