expensive.... i have 13000 miles on my 355 and had to do the major service which has to be done between 3-5yrs depending on milage etc europe say 3yrs north america say 5yrs anyway service runs about $5-6,000 i added a tubi exhaust which i got a deal on and cost $2800. the only problem i had was i had to replace one of the ECU's at a cost of $2800 i get the car serviced twice a year and it costs around $1000 but if anything goes wron you can bet its not cheap so;
First year if you have to do service $5-6000
upgrades and very very expensive brake, exhaust system etc
after that $1000 each service and keep your fingers crossed
they also eat rear tires and i am told F1 gearbox on pre 2001 cars if the pump goes its $15-18,000 yes you are reading right.
good luck they are great cars and so much fun.