Just how big is your house and what kind of carpet are you buying?
Try Carpetright. We bought a carpet similar to their Dynasty Twist carpet, currently retailing at £8.99 per square meter.
UKCarpet mills currently do underlay from £2.89 per square meter.
I know we got fitting quotes both from Carpetright and directly from independent carpet fitters. (Like the ones contracted by companies like carpetright).
The independent fitter advised us on underlay for that carpet, as did Carpetright.
But ultimately we bought the carpet from Carpetright and bought the underlay where the independent fitter advised us (not directly through him, but we "mentioned" his name.) And the independent carpet fitter fitted the carpet.
That was 18 years and 3 children and 3 dogs and lots of sleepovers ago. It's still looking good, but we will probably replace it in the next 2-5 years.
But absolutely no way will I be spending £2K to re-carpet our home.
PS: Find a neutral colour and carpet your entire house in that one carpet.