WizzAir is offering return flights from Dortmund, Germany to Reykjavik, Iceland for as low as $45! That works out to a cost of just about 1.64 Cents (Pence) Per Mile flown.
The fare only includes carry-on luggage, so you will need to pay extra if you want to check-in bags.
Prices change with the selected dates and with whether you have a Wizz Discount Club membership. August and September 2020 seem to have the most dates with good prices. Here is a sample itinerary in August (Aug 12 – Aug 19):