How much do window cleaners cost these days (London area)?

[naturelover]

OK I usually only wash the windows twice a year but we've just moved into a very grimy house and I've got my work cut out trying to keep on top of normal jobs while renovations take place, as well as running around after a toddler, doing freelance work in the evenings and being pregnant! I figure if it's not too expensive I might splash out on a window cleaner as a one-off. The windows and frames (upvc) are filthy, inside and out, but I figure I'll do the inside myself. In total we have 7 windows.

Ballpark figure, anyone?

I pay a tenner for about 6 windows, front and back.

I pay 14 for 4 bed semi.

I pay £7 for just the front, 2 bays (3 windows each) and front door and side glass panels.

That seems reasonable, thanks everyone. As a one-off I think it will be worth it. We can barely see out! I honestly don't know when I would have time to do it myself in the coming weeks.