When the AC compressor went out in my '03 Suburban, I purged the system and replaced everything myself. Not too bad of a job if you take your time and make sure everything in the system is clean/flushed of debris. Doesn't take much to clog up the orifice tube, which will require you to evacuate the system and start all over. Get all new seals, after you purge the system, pull a vacuum and ensure it holds for a period of time before recharging. Since the system is completely empty now, ensure you are refilling with the proper amounts of oil and refrigerant...i.e. weigh them, don't count on the box measurements.
If the A/C lines have been disconnected and exposed to the environment, you'll need to spend more time flushing the system to ensure it's completely free of debris, dirt, etc.
I believe when it was all said/done, I spent around $400-500 on parts and supplies (refrigerant/oil) and took about 2-3 days (part of which was holding the system under vacuum to ensure there were no leaks) which was a pretty good deal, compared to the $1500 I was quoted.