Santorini is absolutely gorgeous. My wife and I stayed in Fira for 4 days in early April and found this to be a wonderful time of year to visit. If you're into photography, then early April is the absolutely best time of year to visit Santorini. The streets and pathways were nearly empty, yet there was plenty of shops and restaurants open to keep us busy.
We stayed at Pantelia Suites in Fira and found this to be one of our favorite hotels in the world. My wife and I have traveled extensively and service at this hotel was next to none. The hotel's location is perfect. It's close enough to all of the restaurants, shops and bars, yet it's tucked away in a quiet area. The view from Pantelia Suites is to die for (check out the pics below).
The food in Santorini isn't outrageously priced and is comparable to what you would pay in any major city in the U.S. If you're on a budget, there's a number gyro shops in the center of Fira where you can get two great tasting gyros and 2 beers for less than $10 U.S. The restaurants we ate at were all very good. Again, if you're trying to save money, simply eat at some of the restaurants without the caldera view. The food will be just as good or better for nearly half the price.
I definitely recommend renting a car during your stay and explore Oia, Red Beach and the rest of the island. The price of the rental car was around $60 U.S. for the day.
You can check out my pictures of Pantelia Suites and the rest of Santorini here: http://flic.kr/s/aHsjuv6gDp