I'm hoping to travel to Sardinia from Naples or Rome in the next few days, and can't find any airline that flies from Naples to Porto Cervo. Can anyone point me in the right direction. I'm also looking to book a hotel with a pool. I don't want to spend more than 250 euros a night. Any suggestions would be greatly appreciated.

Alitalia and Meridiana have direct flights from Naples to Olbia. From there I'd rent a car and go to Porto Cervo.
Porto Cervo is a ritzy area, so prices can be very high. I know that Melia has a hotel there in PC which is beautiful.

BTW, the reason why I said to rent a car is that Sardinia doesn't have a great public transport system, and the whole costa smeralda from Olbia to Stintino is GORGEOUS, but it's better to use a car to see it because so you can stop along the way.

If you have a car and want to be near the Costa Smeralda, but not in the heart of it, I would recommend this hotel:

http://www.roccesarde.com/

I stayed at "Il Piccolo Golf" last September, just 5 minutes from Porto Cervo. It was such a good hotel for the price. It was about 70 euros a night, with a pool. It was so cheap and clean. I booked this hotel at the airport hotel counter when we arrived at 11pm. We hired a car through driveaway.com.au. It was a great company to use, the car hire was so cheap.