Unknown Refrigerant Removal

I have been told it should be less than $50 to have my refrigerant collected? This is not a usual service I see advertised. I was told by PO that R12 was converted over to R-134a but car still has original correct R12 sticker. I cannot fix my grinding compressor (clutch bearing seems ok). I just want a new compressor but my system is still charged. Will a shop refuse to service my car if I can't 100% tell them what is in it? Is there a test? 1982 corvette