AC recharge on 1992 Chevrolet Caprice

Took my car to Sears to recharge my AC and they informed me they no longer have the freeon to use on my car and that I would have to replace my AC parts to comply to the new freeon They gave me an estimate of $600
How much more expensive is R12 to install and is there another way (inexpensive) to fix the AC

Asked by for the 1992 Chevrolet Caprice
The original refrigerant was R12 the more modern replacement is Refrigerant R134. They want to retrofit the newer refrigerant. R12 is still available but is very expensive. To retro fit the newer refrigerant they have to evacuate the air conditioning system, flush the system, check for leaks and repair leaks as required then change the high and low pressure charge fittings and refill. The quote they gave for all of this work sounds fair if this is what they are propossing to do.
r12 is available in mexico still, it is one of the most common illegally transported item, that makes it easier at $8 a can....