Do not sale yourseft short,call your local truckwash and see what they charge for washing school buses.Its better to wash a few at a higher price than to wash several at a low price,stay in the price range as your local truckwashes.Personally I would want 30 for outside wash and windows,sweeping would be extra.Use a soap made for washing fleets,usually the higher price soaps are better but not always true.

Lowballing the price will get you nowhere other when working 7 days a week to make ends meet.

When In Doubt Think It Out