Hi,
first of all there are some grants available from seai.ie - you might be able to qualify for these. So check out:
http://www.seai.ie/Grants/
I only use oil as I can't get gas where I am... The burner you get needs to match your house size / number of rads etc. From what I've read, firebird are about the best, a bit on the expensive side, but I think it's worth it.
From what I can guage, you should have the new oil boiler installed for under €2K (others may be give you specifics here regarding price) - if you are going down the grant road, then you need (AFAIK) the TRV (termo rad valves) and zoned heating controls aswell - zone for upstairs heating, zone for downstairs heating, zone for hot water only. You need to offset the cost of the zoning against the grant you are getting to make a call if it's worth it for you.. less work that the plumber needs to do, less it's going to cost you.
Get a few quotes ok, around 5 to be competitive... ask questions & note what you are getting for your money, size of boiler / type of, etc.. if you can get a recommendation from someone all the better - there are a few people out there that are not qualified - ask for qualifications, check them out - they should be registered. I had 2 guys out who never returned with quotes when I asked for qualifications / what boards they are registered with... I'm in the Cork area & can recommend someone if that suits. Remember that the cheapest isn't always the best... you may also find that it'll be a good time to flush out the system, replace a few rads / connections... remember it's cheaper to do that now that later on.. so if you have concerns on a rad(s), then ask for costings to replace them aswell...
As an aside, the gas boilers are more efficient than oil, but you should be pushing for the highest boiler efficiency than you can get... at LEAST 92% in the case of oil burner. Also, with the gas install, if you are getting this, they must be registered as gas installers... check the bord gais site for info on this...[broken link removed]