How much is a unit on its own though? I think a lot of the total (I.e., installation) cost comes from the fact a lot of houses need larger radiators, re-piping, if the house is in any way modern it probably has a combi setup so will need a complete re-plumb to add (back) in a hot water tank...it is a good question and one i have wondered myself. I always assumed it was economies of scale and they would come down.... but apparently this isnt the case even in countries where they are used quite a lot. (you would have thought if it was economy of scale it would have had an effect there)