Depends on where you are. In SF, you're looking at a minimum of about $200 an hour (for a fairly inexperienced lawyer, who will take longer). If you want a 10 year lawyer who actually knows what he's doing, you're looking at about $300-$600 (depending on experience, what kind of firm he's at, etc.). Lawyers don't read much faster than you would, so you can basically do the math on what to expect, based on the size of the stack of documents you want read.

If it's a three page contract, and you don't have an existing relationship with the attorney, you'll probably just be charged a flat fee of a couple hundred bucks, or nothing, depending on what sort of other business you might bring in.