R-12 is coming down in price as the number of conversions of old systems increases (and some of the old cars die off) and demand decreases. I paid $15/12 0z. can for multiple cans last Saturday. Typically I'll use Duracool or Envirosafe (actually I mix my own propane/iso-butane...eh, close enough) as a "test" on an older car with an R-12 system. Pressure tests, leak tests, fan performance can all be checked with the HC and the system totally verified. Then I can barbeque with the HC and do the "final" charge with R-12.
The Golden Rule
1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)