In answer to some of your questions:
In the Boston area, typical mastering rates range from $80-$120 per hour. That does not include Gateway Sound in Portland, Maine (Bob Ludwig) which would cost substantially more.
You did not say what recording system you are using, and what you mix down to. If you are mixing to analog (1/2" tape) you simply send the tape. If you have acess to a Masterlink, you might be able to send 24-bit audio CDs, providing the Mastering Facility can use them. I usually burn data CD's with 24 bit files, (either AIFF, Sound Designer, or WAV., depending on what they ask for). Actually, this part is easy. Once you find a facility you wish to use, just ask them what they want. They'll find out what you are capable of giving them, and they will pick the best option, and tell you exactly what you need to do.
You should, of course, compress, eq, pan, and set appropriate volume levels on your individual tracks in a session. That is called mixing.
What you don't want to do is try to do the Mastering Engineer's job, because all you will probably do is make their job more difficult or even impossible. This means going VERY EASY (if at all) on any processing done at the 2 buss/Mix buss level. And LAY OFF the Finalizers or other equivalent hardware or software!!!
With all respect to Blue, since he admits to not being a mastering facility, I would first explore other options. They are pretty ubiquitous - it shouldn't be hard to find a legitimate place. Mix magazine has a annual listing of places sorted by geography that you might want to check. If you need a dentist, go to a dentist - not a veternarian or a podiatrist.