I stocked up on R12 back in the day when it was still legal for
anybody to buy, and that's been pretty helpful over the years in being able to
stay with the old stuff - which is both colder and doesn't have as great a
tendency to leak with its smaller molecules. I have enough that I don't think
even my great-grandchildren will run out.
I note that Ebay still has a lot of sources that run about $20 a pound,
so you can actually fill an entire system for less than $100. Of course you'll
have to buy it through your local friendly licensed refrigeration guy, but
that's not too hard to do if you offer to front the money for him.