A real conversion involves replacing most of the components, such as the hoses, receiver/drier, etc. You can keep the evaporator/condenser but they need to be flushed extremely well. The big expense on a first gen is the compressor, which likely needs to be replaced with the FS10 model, if it is one that comes with the FX-15 compressor. It may work for a while, but it's too weak to handle R134a and will eventually go out, probably in the manner of 'black death'.
You are probably looking at north of $1000 for a shop to do everything, labor plus parts and markup. You can save a ton of dough if you buy the parts yourself and replace them, then have a shop do the vacuum and R134a charge if you don't want to mess with that.
Advance Auto Parts still has online coupons giving up to 40% off when you buy stuff online. I bought the 'four seasons' brand of hoses and parts (the only option these days really). Everything together only costs ~$150 with the discounts. A new FS10 compressor from Ford is $200, or you can get aftermarket or used for less.
After that all you need to do once the system is evacuated (or already empty) is just take it all apart, flush the condenser and evaporator, install the hoses, new orifice tube, green O-rings, etc. Once it's all together drive it to the A/C shop for a vacuum and charge and you should have working R134a A/C.
I'm not sure what shops there would charge for a standard A/C recharge, but it shouldn't be too much as R134a is still just $8-12/lb. There are plenty of shops that gouge though, so it's best to check around. It lasts IF you use the green HBNR O-rings and the barrier hoses made for R134a. Systems that just 'convert' by putting R134a into an R12 system don't last because the rubber O-rings don't seal as well, and are typically leaking already anyway. Replacing them with the green ones helps, but R134a will still 'leak' through the R12 hoses.
