If the fabric has been provided, then if I were you I would just keep track of the hours of work you put into it, and charge an hourly rate that you think is fair. Not sure what the minimum wage is in the US (if thats where you are?) but remember that cleaners and manual workers get at least that, so your skilled work would be worth more than minimum wage. Add on the cost of any of the materials that you use of your own (thread etc) and then add on to all that the profit you think is fair...which all depends on who you are making it for, how much they can afford, and how much you like them!
Hope this helps.