Apologies, it's not exactly DIY but I thought you would know best.

I need to replace a single-unit kitchen window, door and surrounding
frames etc. They're rotten and falling to bits. For speed and ease,
I've called Everest windows to come and give a quote on Weds morning
but I would like to be forearmed. Can anyone give me a rough idea of
how much it ought to cost? We're after a double-glazed door and window
with wooden frames, as befits a traditional North London terraced house
conversion. Any thoughts and suggestions are most welcome. Thankyou!