£350 sounds about right to me. I just had a single sash made (not the whole frame/thing - just the sash that goes up and down) and that cost me £150 fully glazed. The biggest problem I had was getting hold of a carpenter prepared to do a relatively small job!
I've been looking for instructions on how to apply wet-dash. This is for patching the existing wet dash on my house. Can anyone point me to a useful website, book or simply tell me how to do it ??!