Rich, if you can produce a certain level of productivity then you'll both know roughly what to expect from X hours of your time on site. The longer you're there, the more efficient you are as you only have to set up and pack away once. Getting started is the hardest bit about winning these customers!
The hourly rate is not a negative at all! You can use it as a sales tool - sliding scale, and hammer it home that you can clean much more if you do work all in one part of the building.
The way I got my foot in the door with the nursing home I mentioned was from a one-off small job at an agreed price. When asked to quote for further work, I offered two pricing structures; a rate per metre and the hourly rate.
To be honest, I don't think he considered it that much, he never actually agreed to either price plan - he just rings me and I send a bill, which is always paid within about 10 days. He was happy that I'd showed him a very good level of service initially so he trusted that I'd continue to do the same... I continue to make a 100% effort to be as productive, flexible and helpful as I can, and we have a very good relationship now. If my productivity or quality dropped in relation to the time on site and invoice level he'd soon cotton on!
A manager purchasing contracted-in work needs to know he can hand things over to you and it's done, sorted, in capable hands, safe, no hassle, results every time. Talk to your contact at the hotel and find out what they really want, what's important to them, what they fear.