It's not necessary to rent a car to get around but it makes it much easier. The buses do not run late into the night and the taxis can get expensive, so we opted for the car.
All of the rental places I called will pick you up at your hotel and bring you to their office. You can drop off the car at the airport.
A compact car is typically a Suzuki Ignus (looks like a small version of the Samurai) or Yuris and the subcompact is a Suzuki Swift. Avis considers a Toyota Corolla one size larger than compact.
The main rental choices and weekly rates are:
Avis 322-2889 Compact $329.95, Sub Compact $319.95
Budget 377-7405 Compact $336
Orange Creek 323-4967 sub compact $300
The quality of the rental cars, at least at Avis, is not up to the typical rental cars in the US. The Toyota Corolla we rented had 68,000 miles, a loose door and a tire with a slow leak. We turned that in after 4 days and I talked them into upgrading us to a Taurus. It was in better shape. It had 48,000 miles and no real problems.