R12 doesn't cost $2000 for enough for any car, but if your evaporator was bad, it was bad anyway. 134a may make it fail a bit sooner, but it was going to fail anyway.

R12 is expensive compared to 134a. But the labor that you pay for AC service puts the difference in refrigerant price to shame. Who cares if you're putting $100 worth of refrigerant into a car rather than $20 worth when you're paying thousands in labor?