How much would you tip for tours costing 300-440 Euros?
What kind of tour? Is the tour guide the business owner or an employee? And, surprisingly, where in Italy?
It is like all tipping - very dependent on the service provide. Americans tend to be a bit for generous because of our tipping culture. All things being equal and assume the driver did an outstanding job and it was private tour, probably in the range of 10%, perhaps 30E. If it is a bus driver on group tour with a tour guide and he did something besides driving the bus, I might consider 20E.
You really don't need to tip at all. The driver will be paid a fair wage. Even if he's a guide he will get a fair wage for doing his job. Tipping is an American thing and is not really done in Italy. Don't feel that you need to tip anything. If you want to tip I wouldn't tip more than 10-15 euros. The cost of the tour is enough.
Donna