2001 Corolla a/c compressors?

A mechanic I trust pretty well recently told me that my compressor has seized internally and needs to be completely replaced. But it's a pretty pricey part, and he thought I might be able to find it for a good price online. Can anyone give me tips on how to proceed? Are there especially reputable sites for purchasing these kinds of part? Is this a common problem in '01 Corollas? Do I have any other options?