There are 9 flights from all Berlin airports, Germany to Iceland, operated by 5 airlines. You can fly low cost from Berlin to 3 cities in Iceland.
Reykjavik-Keflavik
Reykjavik-Keflavik
Reykjavik-Keflavik
Reykjavik-Keflavik
Reykjavik-Keflavik
Reykjavik-Keflavik
Reykjavik-Keflavik
Reykjavik-Keflavik
Reykjavik-Keflavik
Check the cancellation policy: Usually, if you choose the lowest fare you will not be allowed to freely modify you flight details later on (change dates or passenger names, etc). If you think that you might need to do this, you should consider buying a more flexible (but also more expensive) ticket.