R-12 (commonly referred to as Freon, a name DuPont owns) was the refrigerant of choice for auto A/C systems for many many years. Its production was banned sometime around 92 or 93 since the government thinks it's increasing the size of the hole in the ozone layer. (it's a CFC) The replacement for R-12 is R-134a, a hydrofluorocarbon (HFC). It's more environmentally friendly and has been phased into auto A/C systems since the early 90s. R-134a isn't as good of a refrigerant; it requires more compressor power to produce the same cooling effects as R-12.
Supply and demand has caused the price of R-12 to go up (since it's not produced anymore) to probably over $30/can now (I haven't had to buy any since 95), and you can't buy it without a license, which wasn't the case years ago. R-134a is relatively cheap, about $6/can at any auto parts store (or Wallyworld for that matter).
Tyson
95 LS (for sale, R-134a included)