any ideas?

Hi There
I just bought a 1998 3181 BMW and the aircon is playing up.
I was aware of the problem when I purchased the car.
Can anyone tell me if they have had this problem: Air-con works though inconsistant.
Meaning sometimes it is hot not cold and the compressor makes a funny whine.
I have taken it to two places and the difference in ideas and quotes is astounding.
One guy said"yeh mate have it on the road again for $2500"
The next guy said it may be overgassed and would only cost $150 to fix(if indeed that was the problem)
So any one out there got any thoughts?
I love the car but I think some of theses people see BMW and think I'm Rupert Murdoch.
Kind Regards
Dirk Hunter

IF the compressor is bad it will cost some money to fix. It shouldnt be as high as the first estimate. I doubt it is over pressurized. It might be but hihly unlikely. Usually the compressor goes out but it makes noise when it is too low on refrigerant. It clicks and turns on all the time. Describe the noise more. By the way I am hammered.