JT76 - that's ridiculous money. Runcent Joinery made my box & sash window for about ?475 each incl. VAT, and they're about 1.5m x 2m. That's single-glazed, primed and ready to fit. I fitted them myself, but it's no more than 1/2 day's work per window (and mine were pretty big), followed by a return visit perhaps to 'make good' ie.fill/plaster/prime ready for decorating. So even if you're being quoted a grand you're being well stitched. This is bread and butter work to any decent builder, if they have trouble considering this job as otherwise they are cowboys. If it's double-glazed panels you want the only additional cost should be the extra glass cost. Runcent Joinery do measure if you ask them (not always straightforward if you haven't done it before). They also fit I believe. Some people on here don't rate them but for me they're great. You may be better off getting the window made ie. you could get a firm like Runcent to come measure first (week or two to make it, if there's a queue). Then look around for someone to do a straight fit (try see if they do it/know someone ?). If the window costs say ?300-400ish, I'd be surprised if a builder willcharge more than ?300 to fit as he won't be there long. Getting the old window out is less than an hour once you've got your dust sheets down and tools out, fitting is about the same for such a small window.