What I meant exactly is, give an estimate and an hour quote. Let the client know that if you complete the project in less time, you will charge less and vice versa. I've found that in all projects specs change and things take less or more time than estimated. Nothing sucks more than working free because you underestimated a task. Also if you have a fixed price, you will invariantly be motivated to take the quick and dirty solutions everytime. This will not lead to success for the project.