I just stayed a week at the hostal 'La Isla' in Mahon and can only recommend it to anyone!
The hostal is like a B&B type set-up and just excellent value for money.
I went there pre-season (end of March), so, obviously, everything was fairly quiet - which is exactly what I was looking for.
The owner, Paco, and his family are super helpful and friendly and I cannot wait to go back there again.
The hostal is located in the old town part of Mao and rooms are very nice, functional and quiet.
As I said, this is a fantastic place and great value for money, if you're looking for a great, clean, friendly place on a budget.
Two very entusiastic thumbs up y'all!