Again small local firm where you can get to see the MD, who takes an interest in the customers before seeing them as a wad of money.
I can give you a costing if you send me your sizes, or as a rough guess price each window at £350 (as long as they are not massive!) and a single door at £700, double doors at £950, add a bit, say 15% and that should get you a ball park figure from a small local company.
If you go to one of the big four you can double them prices, maybe treble and then wait for the hard sell....... "If you sign tonight I can give you 15% off", or, "Your not happy with the price, let me phone my manager to see if he can ok a discount for you", or, "The rep couldnt make it tonight so I had to come out, I'm <salespersons name> manager, I dont want to be here so I'll give the best price straight out" or, 'Show home discount', or, 'group scheme discount', or any other tawaddle they can dream up.
All bigger companies use closers, top sales people who close deals, the commission on these deals is usually on a sliding scale, maybe 15-20% max if the deal is sold 'out of the book' top money, the more discount they give the smaller their commission.
Imagine a £10k deal sold at top money, thats at least £1,500 to the salesman before you see your windows!