A condensing boiler is a kind of combi boiler as far as I know - unless I'm just being slack on the terminology! Certainly if the OP is using the term as distinct from the sort of boiler that has a big hot water tank then a combi and a condensing boiler are effectively the same.
Mine was probably about the same sort of price - dear, but much more efficient so greener & cheaper to run. Or you could consider solar hot water as an option?
I haven't bothered getting a maintenance agreement - it wasn't Brit Gas who installed it but rather a local indie supplier who services it regularly. If it's new it should be under guarantee for a while and if it's regularly serviced it shouldn't go wrong...
We are looking at boilers right now as ours is on its way out. We are covered by BG and the cover has been worth its weight in gold to use, so I don't begrudge the £23 a month we pay. Each time we have called them they have come out the next day and fixed it, but the parts are no longer available.
We will be getting a local (recommended) plumber to install it and I wil let you know how much he is going to charge us when he rings back.
I don't like combi boilers so we are getting a heat only one which will have a 5 year guarantee so we shan't renew the BG contract until that runs out.
WE got a combi boiler fitted last year. Ours is a big one and we got it (fitted) for £1550! I checked out the prices to buy the boiler I wanted online, and told the gas fitters that when I called them. i explained I basically was looking for their price to fit it. We had some much higher quotes, but the guy who ended up doing it (who was really good) said he needed the work and cut his price accordingly. So always worth getting a few quotes- they can vary remarkably
2.5k with thermostatic valves for a Bosch Combi v. big one (not very technical!) 18m ago but depends on number of radiators/size of house. Used a respected independent heating co., BG always more money.
Have now had formal british gas quote which is £2700. They advertise the cheapest boiler as £1700 but chances are it will come to more as the house of mirth says. We were unable to haggle with our salesman so are getting other quotes.