Hi, Unfortunately marine engines and everthing else connected with the marine industry is and always has been expensive and while I agree that they actually have gone up significantly in the last year due to the sterling- euro exchange rate drop (blame the government), in relative terms they are probably still alot cheaper that they were 20 years ago when we all earned 10 quid a month!
I think it's a great opportunity to keep running the older O/B and actually look after them, as when they are looked after they will last a lifetime. My dive clubs 2s Yam 115 is a 1994 engine and looks almost mint, its been very well looked after and apart from gobbling fuel is as smooth as silk and is 100% reliable!! mmm that's a dangerous statement.
I agree it's tough if you need a new or bigger engine, just a thought but could you import one from the states, a colleague did that with a bayliner boat a while back and it was certaunly cheaper than buying the same craft in the uk. I also sometimes buy boat bits from the states via the internet.
As one of the other contributers have said, marine engines and cars are very different because of the different volumes involved, just look at the costs of running a small aircraft. All the spares are very expensive and not really because they are anything special in terms of technology its just the volumes and the bull shit that they are manufactured out of special materials and are genuine OEMs etc.
I intend to keep my old smokey Merc going for as long as possible as its, light in weight, cheap to maintain, simple and I can understand how it works and generally fix it myself, using a merc workshop manual.
Just my thoughts.