The cheapest flights I've found so far:
http://www.norwegian.com/en/
1st Choice:
London Gatwick to Oslo-Gardermoen
Leave - 0840hrs (13th) Arrive - 1200hrs (13th) Spend night in Oslo.
Oslo-Gardermoen to Bardufoss
Leave - 1315hrs (14th) Arrive - 1505hrs (14th)
Bardufoss to Oslo-Gardermoen
Leave - 1415hrs (20th) Arrive - 1605hrs (20th) Spend night in Oslo.
Oslo-Gardermoen to London Gatwick
Leave - 1810hrs (21st) Arrive - 1930hrs (21st)
Total Price (Including Taxes & Surcharges): £246.40
2nd Choice:
London Gatwick to Oslo-Gardermoen
Leave - 0840hrs (13th) Arrive - 1200hrs (13th) Spend night in Oslo.
Oslo-Garderdmoen to Bardufoss
Leave - 1315hrs (14th) Arrive - 1505hrs (14th)
At end of course spend a night in Bardufoss.
Bardufoss to Oslo-Gardermoen
Leave - 1530hrs (21st) Arrive - 1720hrs (21st)
Oslo-Gardermoen to London Gatwick
Leave - 1810hrs (21st) Arrive - 1930hrs (21st)
Total Price (Including Taxes & Surcharges): £254.10
These are of course just prices for a single person flying Economy Class.
For the nights in Oslo I have found this hotel, which if we share a room will be very cheap.
http://www.budgethotel.no/oslo/english/index.php?id=2
I'll be taking the first option if anyone wants to travel with me.
I hope this is helpful to some of you.