I was in Oslo a couple of weeks ago (courtesy Ryanair) and can confirm the prices, except my beer was £10! I might be invited back, so I'm thinking about the GA options.
Are there any affordable GA fields near to Oslo with convenient connections? I flew Ryanair into Torp and out of Rygge, both very small places a long long way from the city. I didn't see any private aircraft at either place, but it was dark at Rygge. I'm thinking that an alternative that I've been to before might be Hagfors in Sweden (very friendly GA field, not much further from Oslo than Torp) and a rental car, though a car would be a nuisance in Oslo city.
Any ideas appreciated.