You make some very good points and I am planning to keep Freon12 in the car as long as possible and am hoping your pricing scenario is correct. This was kind of a contingency question in the event that the cost of Freon became prohibitive.
At the shops that I have been to here, Freon is quoted by the pound and is currently $50-65. With labor it cost me recently $125 to have 1.5 pounds charged in. I have had the 560SL since new in 1988 so know the whole history of the car and the mechanic was amazed when I told him that was the first time it had ever been charged. Probably would still be getting by without the recharge if I hadn't moved to sunny New Mexico from New York. The AC was seemingly doing OK there but couldn't keep up with the heat here.