R-12 replacement

The A/C on my '92 Metro could use some servicing.
It will still keep the car cool, but not like it used to.
It has the R-12 refrigerant, and most likely needs a small amount added.
Finding someone to service R-12 seems to be next to impossible.
Everyone says to convert to R-134A.
That's where I'm getting conflicting information.
I've heard everything from "just remove the R-12 and add the R-134" to replace compressor, seals, fittings, dryer, orofice tube, hoses and totally flush the entire system.
Estimates from $100.00 to $1500.00.
What is actually required to replace the R-12 with R-134A?
Thanks,

Seriously all you need to do is get the retrofit kit, evacuate the old out and refill with R134. It will be fine. I have retrofitted many vehicles with no problems. Changing the dryer is not a bad idea.

Seriously all you need to do is get the retrofit kit, evacuate the old out and refill with R134. It will be fine. I have retrofitted many vehicles with no problems. Changing the dryer is not a bad idea.

I asked one shop about this. They called it a "dirty conversion" but said that they would be willing to do it. I had planned on changing the dryer, but am curious if the R-134 requires a different one than the R-12.
thanks,