charge about £60 if its avarage size , get some trafic film remover like autosmart or active 8 , wet the hole roof first them spray on this stuff rub in well then rins off.
do not let it dry on ,in some that i have done you have to wash the lot down sides gutter everything ,if so charge £80 .
the decaretive mouldings on top can be very fragile so take care with the brush on them . the spike thing needs careful brushing .
if you go to your local car wash they might let you have some, autosmart is the name of the out let for this.
never use power washers they nacker the seals on the roof so all you need is pole with good stiff brush ,not bass broom .
good luck

oh and stick by the price you give i know it sounds a lot but they do pay this sort of price to me. in some cases even more if they are big ones.