If the compressor is bad, that means you have to replace the compressor, the expansion valve/orifice tube and the reciever-dryer/accumulator. That alone will run you $300 or more in parts, about $100 in refrigerant and oil if you convert to R134a, much, much more if you stick with R12, and somewhere in the middle if you go with Freeze-12. You'll want it done at a shop that has the right equipment and certifications, so throw in the labor at $75-100/hr, and this is an all-day job. You're looking at $1000 or so, and that's just if it's the compressor.
If it's the Evaporator, they've got to take the dashboard apart to change it out, and still have to do the same thing with vacuuming down the system and replacing the refrigerant and oil, still looking at about the same cost.
If it's the Condenser, it might be a little cheaper, because they're very easy to get to on these cars.
If it's hoses it'll still be expensive because they are hard to find, and they may even have to buy bulk A/C hose and fittings and make them themselves.
A/C work is always expensive, and it's hard to get all the parts together for these cars due to their age and relative lack of popularity.
__________________
1976 Ford Mustang II Ghia: 302 with a 600cfm Edelbrock carb, Edelbrock Performer 289 intake, Dynomax Blackjack headers, 2.5" exhaust with Flowmaster Super 44s. RJS 11-gallon fuel cell, C4 tranny, chrome 16" pony wheels, fuzzy dice, brown vinyl half-top, and painted in the tackiest color ever (harvest gold, that's why I call it "The Goldenrod").
Also have a 2003 Dodge Ram (lightly modded daily driver/tow rig/office/dining room/home away from home/workshop... I call it "The Big Blue Dawg".)
Thanks , that really helped, i think it might just be best if i didn't have air conditioning then.
Yeah, my '76 Mustang's A/C system is all there, and all original, and doesn't work... it'll be the last thing fixed... My '75 Chevy doesn't even have any of it's A/C system anymore except for the control head and the heater box. Just not worth the money to fix it, not even here in Texas. (besides, on that old truck, opening the vent windows works wonders!)
__________________
1976 Ford Mustang II Ghia: 302 with a 600cfm Edelbrock carb, Edelbrock Performer 289 intake, Dynomax Blackjack headers, 2.5" exhaust with Flowmaster Super 44s. RJS 11-gallon fuel cell, C4 tranny, chrome 16" pony wheels, fuzzy dice, brown vinyl half-top, and painted in the tackiest color ever (harvest gold, that's why I call it "The Goldenrod").
Also have a 2003 Dodge Ram (lightly modded daily driver/tow rig/office/dining room/home away from home/workshop... I call it "The Big Blue Dawg".)
I have my air conditioned fixed for just few bucks so It was ot big deal only just properly tigth a hose that has a little leak and replenish the R12 gas . I live in mexico and labour and gas is not as expensive as it is in the US .
My AC it is an aftermarket adaptation and cools very good ( it brougth this when I bougth the car) the only problem with it is in low speed or in down town traffic , it heat too much the engine.
I do live in the yucatan at mexico and its is very hot down here specially in summer. An AC its a must down here.
1974 Mustang 2, How much for airconditioning 
