Lisa,
Robert is much nearer the true price of the job than you.
I'm sure his form will show you Basic pay, holiday pay, sickness allowance, NI contributions, clothing/uniform, marketing, travel/vehicle costs, cleaning material costs, supervisory/managerial costs, etc.
Then, at the end of the day you are in business to make a profit.
Rob, could you send me a copy and I'll reciprocate to see how much our costing formulas differ by.
Cheers