For $550 you could buy everything you need to recharge with R12 legally and have about $400 left over.

Start by going to www.imaca.org and spending $15 to take the online test for a 609 certification so that you can purchase R12. Then go on ebay or some other source and buy 3 cans of R12 for about $45 and that still leaves a bunch of money for a set of gauges and an auto a/c book.

Regardless of your choice, you will decrease a/c capacity by changing to R12 and be going to a refrigerant that may very well be as expensive as R12 next summer.

Stay with R12. It's the only thing that makes sense today.

Good luck,