You could easily install a new compressor if you wanted to but even if you don't, that much labor is suspect.

Also, the general rule for refrigerant is 2-4 pounds per ton. So he might be on the mark at 15 if you have a 5 ton system. But you are right that they mark up refrigerant like crazy. Tell them you are going to provide your own tank. If they won't do it, find someone else.

You can find an a/c contractor that does work on the side pretty easily if you look. Post on KSL or Craigslist (or whatever resources where you live) but be sure to check certifications. To some people that might sound risky but if you watch what they are doing and get the right guy you could literally save 75% or more on labor.

If that doesn't appeal to you, at least get a 2nd and 3rd opinion. Tell them to drop the bogus charges. Just like a car dealership with their doc fees and processing fee and all that.