Mastering is to mixing what coitus is to foreplay.

1) Read the above posts, and pay special attention to the details in Deb and Mick's posts.

2) Do NOT let the person doing the mastering over-ride what you want. It is your CD.

3) There is too much overly compressed stuff out there. Don't let that happen.

4) Be there at the mastering session.

If you've done a good job in the mixing process, mastering time should be proportionally less expensive. From what you describe, CB, it should come in about $300-400.