Alpenlite DL
From what you have said, I can tell you that the problem with your A/C unit is either very minor or very major.
Very minor would be a bad electrical connection, thermostat, selector swithch, or compressor starting component. Any competent technician can eliminate these potential problems in about a half an hour and give you a firm price on the fix.
Very major would be a bad compressor or a refrigerant leak. A new compressor can easily cost as much as a whole new unit by the time it's installed and running. A leak could be worth working on, but the cost can climb quickly. Like I always said, if you're going to pay for a new unit, get a new unit.
Ed