I have asked two dealers and two specialists for a quote. The price range was from €2800 to €1350 for a major with belts, but without valves.
The best known specialist in NL is
Franco. It is a 2 hr drive for me to get there, but I think that it is worth it.
He quoted me the best price, and has 27 years of experience on Maserati's.
I thought about bringing the car to the uK for a service. The £ is very low against the €. But the total costs of bringing the car there, spending the night and drive home would be about equal to the costs that I am making now.
But I did look for prices on the websites of Verdi, DK Engineering and some others.