Sardinia tends to be a bit expensive in summer, but it depends where you go. The areas around Porto Cervo are probably the most touristy, with lots of local and foreign VIPs spending their holidays there, which results in prices being hugely inflated. I would suggest to try the area near Alghero, which should be cheaper, but neverthless beautiful. The best way to see Sardinia is to get a car and check out the many different beaches/coves on your own, so you can something different everyday. Also, taking a boat trip to some small islands is a definite must, especially to La Maddalena.

its wery beautiful there, I enjoid it lot