Wow DB price seems very cheap and would require one man to cover about 1250 metres in a day for the price of just over £200 if cladding is reasonably clean and pressure washer can be used then i suppose that area could be possible but i would want more than £200 to do it, if cladding is dirty and a cherrypicker is required as using telescopic pressure washing pole at 7metres all day is extremely phisically demanding and to factor in travelling and diesel etc then i think they have way underpriced the work. If the cladding is really dirty and needs to be done by WFP then you couldnt even price the work without doing a demonstration patch.
These are just my opinions and others may know better but how you can give a price for work like this without seeing the job is beyond my capabilities.