hi Ste.
I see your based up the pool which can be a problem in certain area's because there are loads of w/c 's who are not legit and will charge really low prices so your up against that right away.
I know a legit w/c in Huyton who went to quote a house in crocky 16 windows 4 patio doors and he was told his price was too high £5 ?
I had a w/c approach me and asked me if I fancies doing a days work for him on some 5 story blocks of flats using my van and poles and said there was £60 a day in it for me cash in hand, great when can I start I replied and walked off.
if you know your work is good mate then price it to what your worth for that job, yes you may not get the job but you only regret it if you go in far to low, one thing that may be of help is count all window and round to the nearest £5 i.e. £5, £10, £15
good luck with it