Im not as expeienced as some of you guys on pricing and i agree that the prces depend where you live in the country.
However, i like Ian101 pricing as it is very similar to how i do it - you then look at the price and depending on how it comes out and how easy the windows are to reach etc. you can add or take away £2 or £3 to get the business.
I also would rather come out slightly expensive as you may be undercutting yourself, even a pound or two with each client either way can add up to a lot at the end of the month.
Also if the client doesnt seem too keen on the price you can always say "so how much did you expect to pay ?" jut ask the question and if its a bit less than you quoted you can always drop slightly/come to some middle ground. If they say a silly price then you probably dont want the job, unless you need the work or want to keep the opposition out... the choice is then yours.
Finally, Ian101, are you trad on those prices or wfp ?