The only other Airline I know of that flies to Keflavik is SAS . Keflavik Airport is probably one of the smallest international airports you will ever see. The airport is nicely laid out with an assortment of shops available. Keflavik is about a 30 minute drive from downtown Reykjavik. Near the airport, the US Military holds a significant presence , using the airport as an airbase linking the US to Europe and beyond.
Immigration is quick to clear and there is a money change counter available in the arrivals hall.
Reykjavik is a medium sized town, with 170,000 residents. The town has a variety of hotels. Simple expenses such as dinner are probably second in price only to Japan. Remember - everything in Iceland needs to be imported, resulting in higher prices. Travel via taxi is also pricey, and car rental is very expensive.