there's no "direct" replacement for R-12, because by law, anyone servicing your system for consideration is required to install special fittings specific to the refridgerant used. Due to other factors such as oil miscibility and hose porosity, the CHEAPEST option for most people will be to keep R12. Now, you can find it on E-bay, and if you look enough you'll find an auction that doesn't require a 609 cert#. Illegal for anyone to sell it that way, but it still happens occasionally.
Another option is to go to a site like
http://www.epatest.com and do it legally. You can download the training document for free, then take the online, open book test for only $15 or $20. Plus, you'll learn quite a bit just by reading the information and feel better knowing more about how your system works and confident that you will be working safely, I know I did. Boy, what a great country we live in, with the choices we have!
