A very important question how much does this service cost?
Take the amount you want to in a month and divide by the number of hours worked to get hourly rate. Assign time-based pay per hour/day./a week/that month. If you want a fixed amount, then figure out how long (hours) will take on the project and multiply it by the hourly rate.
How else? No more, just no experience in this area (judging by the question). Will finish this project and you'll better understand how much a pound is dashing.