ignition switch and ac compressor

Two questions. 1. I want to change ignition switch on "92 grand marquis. Do I need any special tools and what is best step by step to do it. 2. I also need to change ac compressor. A local ac shop quoted $700.00 for a new one. Can I get one from a NAPA etc. and do it myself? How much do the compressors cost new? Is it worth it? thanks in advance