We can't answer this (especially with the insane amount of ambiguity provided by your 1-liner).

How much you charge all comes back to how much your time is worth (and how much they're willing to pay if you're desperate for the work).

Are you confident enough to say 'this will take x hours'? If so, then charge per project and let's hope that you're right. If not, charge an hourly rate and give them some rough indication of how many hours you think it will take you.