Since you said flights were so cheap I got a bit curious and did a search for a 7 day trip (admittedly from the airport near, which is small). I was not expecting the drastic difference in prices there though.
http://matrix.itasoftware.com/ To: KEF, RKV March 1 2017, 7 days Unlimited stops/airport changes.
Some of those flights are ridiculously cheap though so you were right.