I'm just back from a week in Sardinia, the weather was beautiful, we stayed in Hotel Margharita in Alghero on our first and last night, it's pretty basic but clean and 5 mins walk from the Old town, where all the restaurants are. We ate in Mirador on Saturday night, it was beautiful, though a little more expensive than other places we ate in, still alot cheaper than here at €25pp. If you are staying in Alghero for the entire holiday I would probably upgrade to a nicer hotel , but I'm afraid I don't know enough to give you any reccomendations. We hired a car and we travelled over to the east coast and stayed in Golfo Aranci in Hotel Gabbiano Azzuro for three nights, I booked it through hotelclub.com. It's a 4star hotel and we paid €36pps for a quad room. Pool, private beach, excellent value for money. There is not a whole lot to do in the town itself though. Great for just chilling out by the pool, beach etc. We also stayed in Hotel Pedralada in Castelsardo for 2 nights, the hotel itself was fine with a lvoely pool area, but there was a musty smell in the bedroom.
WaterWater feel free to PM me if you have any specific questions while it's all fresh in my head.
As already said have a look at tripadvisor.com as you can ask questions on the forum section.
Enjoy.