That's a great question. I will work with the client to determine what we feel to be an appropriate amount of time to spend, per song. This will be based on how complex the project, the number of tracks, how serious you are, and how good you want the finished product to sound. One of my current clients asked me this very question via email, so I came up with this response for him, with timeframes on a per-song basis:
1 Hour (per song) mixing: With one hour to mix, I pretty much just do some touch-up EQ'ing of the tracks, and a few other very basic mixing tasks that I find to be the bare mininum starting point for it to sound good. These are basically menial, un-exciting things to the average musician. But probably very interesting to audio dorks like me. So if you're an audio dork, go ahead and call me, and we can talk geek stuff.
1 1/2 Hours mixing: All of the above. Plus a few extra things like tuning of errant notes on vocals, bass, etc. Nothing major; just a note here and a note there.
2 Hours-3 hours mixing: Allows me extra time to do things like: Check the mixes against reference material, critically comparing your material against the sound quality and tonal balance of your favorite recording artists. Double and triple-checking everything for performance errors that can be fixed or edited.
4 Hours: Includes all of the above. Plus I can get in to some serious editing if you need it. This is where the computer can do some amazing things, and we can really give it a good work out in order to fix things in your performance.
Unlimited time and Unlimited $$$ : I've certainly heard of stranger things. But hey, if yo're in to the Phil Specter Wall of Sound thing, I'm game.
If there's any special gear you'd like to get a hold of, it can ususally be rented. You can try out every guitar amp in town until we find the one that gives you the absolute perfect guitar tone. Hire a guitar or drum tech to tune your instruments, set them up, change the heads and strings, etc. We can get a vocal coach to help warm up and better prepare the singer. We could record in a unique location, if you'd like. Bed & breakfast ... banquet Hall ... Church .. cabin.
You could get all crazy and rent an orchestra if you want. If that's overkill, then we could just call in a couple of string players, and keep layering more and more takes until we can get it to sound like an orchestra.
I'm game to try any and/or all of the above, if you've got the time and the financial means, I'm there.
It's always a good idea. Not so crucial if it's just a demo, or if you'll just be selling a few copies at gigs. However, if you're very serious about it, and hope to sell it or distribute it in large numbers, or to get some serious airplay ... you're going to need to have it mastered by a skilled, professional Mastering Engineer.
A good mastering engineer, or "ME," will lend an objective ear to your final mix, and try and add that last bit of polish, to help enhance listenability across all formats from home stereo to car stereo to boombox to computer speakers. They don't work magic, but if given a solid mix to begin with, they can help give it that little extra mojo and can sometimes even offer some zen-like wisdom to a project..
I have a few studios that I freelance at from time to time that we could rent out for a reasonable fee. I would charge my regular studio rates as an hourly Engineering wage, which would simply be added on to the cost of renting out the studio of your choice. And there are plenty to choose from in and around Chicago. Moon Unit Sound is not the name of my studio. It's the name of my recording services. The place I work out of is very functional, and is desnigned to get the job done at minimal cost. But I'm certainly not tied down to it by any stretch.