In Hawaii, they do get peeved if you drive the rentals out of state.

On most travel web sites, you only get really good rates if you're bundling the trip (airfare, hotel and car), to the point where the package price is cheaper than just airfare alone. On more than one occasion, paying for a package was so much cheaper that I booked (and paid in advance) for the airfare, car and hotel, for a day trip and never saw the hotel.

Don't rent from the airport location, they have some pretty high surcharges.