£280 for the inside of a conservatory roof - If they'll go for that I'd do it
Is that glass only or do they want all the framework done? How bad is the fly cr@p?
Without seeing more of the conservatory it's hard to guestimate a proper price - but if it's glass only it's not going too take to long, I use solution made with pure water and a dash of gg3, mop and squeegie on a pole - straight pulls with a dust sheet over any soft furnishings.
I'f I'm cleaning up the upvc too I bring in the stepladders and astonish upvc creme
If I did more internal roofs I would probably buy a karcher window vac and stick that on a pole.