How easy is "easy" to get the license?

I need to re-do the a/c on my truck; there's no actual leak, but I got some air trapped in there...and it'd be nice to put R12 back in. With doing it yourself, how does R-12 compare to R-134 in terms of price?

Heck, for that matter, maybe I could convert the car back to R-12...the R-134 isn't really cutting it, particularly for this polar bear.