Simply work out how long you think it will take you, times it by your hourly rate, add on any additional costs and profit margin.........and there you have it, your price!!!!!!!!!
Sorry to say it but there is no blinding light that will come down from above to give you the answer. You have to work it out for yourself, if you do it right you will get the job and make money, if you do it wrong you will either not get the job or worse still get the job but lose money.