Ugo Cei, quoting Gerald M. Weinberg on how to set a price for one’s consulting/freelance services:
Set the price so you won’t regret it either way.
This basically means that you should not set the price so low, in order to get the assignment, that you’ll regret it if you obtain it. And you should not set it so high that you’ll regret it when the client is unable to pay it. Rather, you should set it so that you’ll feel about the same whatever happens. You shouldn’t feel too bad if you’re turned down and you shouldn’t feel too bad if you’re accepted, either.