Right, we hired a villa last year just outside San Raphael (half way between ibiza town and san an)
The bus ran through San Raphael every 15 minutes from 8 am - 11pm and there was a resturant, spar etc in san raphael.
If we missed the last bus, we used to get the waiter in the resturant to call us a taxi.
Our villa was a 10 minute walk from San Raphael.
Worked out perfect. We also hired cars for the day, and went off to different parts of the island.