I've settled on accommodations for my last three nights in Iceland. I'm going to stay at Vestri-Garðsauki, just outside Hvolsvöllur.
This place was recommended in Lonely Planet Iceland, and it's in the exact area where I want to stay, about 100 km east of Reykjavik. From Hvolsvöllur I might be able to get a bus to Þórsmörk (which is inaccessible by regular vehicles and is described in the guidebooks as one of the most beautiful spots in Iceland), but I might be too early in the season for the buses to be running. Still, there's a lot of beauty nearby, and being early in the season means fewer tourists. Hvolsvöllur is about 80 km west of Vik and convenient to the Golden Circle. It will also be an easy drive to the airport (maybe an hour or two), so I can plan a stop at the Blue Lagoon before my flight home.