£350 minimum.
?? you'll regret that !!!! £840 minimum . . .
ok, for a 7 x 3 normal window you'd charge a minimum of £1, maybe £1.50, but let's say £1
if it's all georgian then it's gonna take you 3 x what it would plain squeegeeing.
so, 70 x 3 = £210
now, think, each little payne you're gonna have to scrape the paint and the concrete off, then clean.
even if it takes 3 times as long, that's £630 !! . . after doing many builders cleans, I'd go for 4 times. = £840 !!
otherwise, you might as well just clean normal windows and earn more !!