Paul
This sort of work is normally low paid compared to houses, i,m 60 miles from you m& know for a fact if we went in at £700.00 int/ext it would be to high.
I quoted £1200.00 for a school 2 1/2 times the size of that & was miles to expensive.
Theres a contractor nearer to you i know would quote £300 to £400 max. Its a market you only do if you need the work or have employees, some of the prices people say are far to high.
Another school i went, i quoted £95.00 somebody was doing it for £25.00.
Theres an article on here to do with percentages cleaned thats the way most work on this sort of thing, we try do all but, charge a little bit more, then you have a good job. The main thing is it can pour down from start to finish & it would not stop you.
The moral is it can be good but it can also be bad.
P.S. We are doing 11 schools during hols. could not fit in anymore turned down some.
Gary