I was going to say much the same thing. (it's only worth what someone is willing to pay for it.) Rather than be completely repetitive, you might Joel Spolsky's article on a similar topic (pricing software), although it doesn't handle the specific case of contracting (as with boxed software, you have to balance quantity sold with the overall procive), it does talk about some of the general concepts to think about.

Oh -- and it might've been during the dot-com boom, but one of my former bosses said the best advice he was ever given was to charge at least $100/hr -- people treat you different when you're making more than they are. They don't come to you with every little problem. They don't waste your time by expecting you to type everything in from a page that's a 12th generation xerox, etc. (I've gotten paid considerably more than that for a rush job -- the important thing is to make sure the specifications are firm, and to beat whatever expectations they may have of you) In some ways, it's like sneakers -- if you raise the prices, people assume there's extra value in there. (see Joel's article). Never try to compete on price -- compete on quality. (again, see the article).