Hi Blacksheep. Sounds like a nice one if you can get it!
Regarding pricing, sorry cant help you there. However, what i would like to know, is whether these are portacabins being maintained on a site, or they are to be cleaned when returned to the hirer??
If they are empty shells to be cleaned before being hired out again, i would imagine that you would only have the basic shell to clean - washing the walls down etc along with any windows. Howevedr, i would also imagine that you would have to strip, clean and reseal the floors!!
I used to use a product from my cleaning supplier, that was applied by a flat mop, mopped onto the floor. Dont worry about the streaks in the floor, as within seconds it murged into a streak free shiny glossy finish!! - Job done.
But anyway, a little more info on what needs to be done to these units would be helpful, and i hope the above helped a little
All the best
Tim