Shane we flew to Bologna from Dublin. 1.5hr drive to Rimini to where we stayed and a lot of people stay as accommodation is expensive and generally booked out by competitors in San Marino. Rimini is 30min drive from San Marino so handy out.
Yes rented a car as its a must really even though organisers put on shuttle buses to stages and you can bus it from Rimini everyday.
Example of cost:
Flights €110 return
Accommodation for two €230 for 3 nights (loads of rooms in Rimini some even cheaper)
Intermediate car €195 (we got Alfa 1.6 diesel and only used half a tank all weekend)
We flew back via Pisa (3hr drive) on the sunday night as no return flight from Bologna to Dublin until the tuesday and i needed to be back for work.
Tuesday would be the job though as you could go to Ducati factory, Marenello and Imola which are all close to Bologna on the Monday.