I have paid as little as nothing, but given the models a CD of retouched images.
I have paid as much as $100 per hr for a very experienced model.
In general in my area (Southern California) the semi-pro models are asking $75 per hour but are willing to take $50.
A good model and MUA can make or break a photo shoot.
So I am in full agreement with Chumley on the importance of good talent.
I find some on Model Mayhem, and some are referrals from people that I have already worked with. After a while you will build a reputation and people will actually seek you out.