Austin, I don't know if this is the type of thing most companies are willing to pay a power washer for on a weekly basis. When they say the parking lot cleaned are you sure they are not referring to removal of trash/leaves/debris? Something that a day porter or parking lot sweeper would do?
How we bid this type of work out here is we would bid it as 3 separate services and let them choose. The parking lot for Parking lot sweeping services. We would base our bid on a per hour cleaning with a 2 man crew sweeping. 1 man driving sweeper and another blowing out curbs and under cars and inside planters. I would let them know they need sweeping done at minimum 3 times per week.
If you don't have a sweeper it would be a great opportunity to sub-contract a local sweeper and start a relationship. You both could use each other's services.
Then we would bid the concrete cleaning on a weekly basis, bi-weekly basis, monthly basis. I also consider that an hourly bid but I would not place the amount of hours in the bid itself. Instead I would use square footage inside my proposal but make sure you know your man hours when coming to the price.
Lastly, if the customer seems like they have money to spend I would send out a day porter to hand pick the lot during the day. And we charge 25-35% markup on the hourly cost of the employee plus trash bags and fuel.
Good luck,
