Depends on what boiler mate. When mine packed in I went for a Sabre 29HE from Mr Central Heating, cost me £500 inc flu kit in 2009. Ive had 1 issue with it which was the fan switch, cost me £50 last weekend. Not saying its the best in the world but for 8 years and 1 issue...its done well and at the end of the day its only to heat water and keep you warm.
I bought the boiler and had it sitting there with all the documentation, got a local guy to install it for £400 I think it was. So in todays money, I would say £1500 all in. Depends if you want to go down the Bosch route, that will cost you more.