You can save a lot by not requiring that you be present for the mastering session. Precision Mastering on Cole in Hollywood. I've known and worked with him for a very long time, and I think he's worth calling. Great ears, and a damn nice guy. Before selecting a mastering company you need to determine exactly what type of services you need and what type of budget you have.
Many people confuse post production with mastering and mastering with glass mastering.
If you want an example of his work Joe Gastwirt recently performed the digital re-mastering of several of the early Yes albums. It usualy says on the back of the CD that he did the re-mastering. I was told that he was no longer there, and had opened his own facility. John Golden left K-Disc and set up his own shop about a year ago. I am an engineer with a mastering company in the Indianapolis are.