I have never really calculated the running costs as I am luckly able to get the green diesel still (although thats after increasing a lot since I first started with diesel).. (depends on the water
)... servicing cost are apprx.€300 per anum which would include engine oil 20 litres,outdrive oil 5 litres, 2 oil filters, 2 diesel filters. I do the 2 belts every second year,as well as the impellar off hand can't remember the prices for these but I have found a Volvo penta agent whose main work is with Volvo machinery, his prices are not as bad as if you were to have to go to a Volvo marine supplier.
I got a quote from a guy (Joe) knows him to remove the engine change the sump and refit I recall him saying "about €800 if I have no problems" believe me I had problems but felt that I would do a better job myself as the engine bay got a good clean and repaint..
"Go on go for the diesel you know you want to"