Does that include fitting? I bet not.
In general, don't let British Gas fit anything. They're the corner-cutters of all time and their annual service package is a sham.
A fair bit depends on what your existing pipework is like. For example, I got a new boiler a couple of months ago and it cost £2,800, about half for the boiler and half for fitting. But the old one was 20+ years old and since it was fitted the pipework diameter has changed (by law) from half...