What time of year will you be there. We stayed at Il San Pietro last year and their restaurant was great and also had dinner at Le sirenuse which was excellent. both were not cheap options however.

One thing that worked out great was that the restaurant at Il San Pietro was used once every three weeks (June-August) to run a charity dinner night at EUR150pp with food and wine and thus worked out good value for what you got - endless Mimosas and wine for one. I believe a different Mitchelin starred restaurant from the region ran the kitchen on each occasion.

Outside of those two, we ate on the front opposite Buca di Bacco which was solid (the three sisters perhaps?)