Marcie, we don't fly out until the next day so we rented a car but my "itinerary" doesn't have us anywhere near the airport by late afternoon. Rental car companies consider Reykjavik to Keflavik a one way rental so there is an additional fee. I think we are paying around $160 with Sixt for a one day rental; we are staying near airport so will probably drop it off the night before. Sixt is close to dock. Search for coupons, but be forwarned that site is not very friendly and it is impossible to find a phone number wherein someone will answer.

Marc