90 days tourist visit

Hi,
I'm planning to visit Norway by November. I have a visa exception because I come from a country with one of those country agreements. The purpose of the trip is to take a research visit, and I am planning to stay for about 80-90days. So, according to the embassy, I will need a simple tourist permission (of course i have to show an invitation letter and other burocratic stuff).
My main doubt is about the requirements of 'sufficient funds' and return tickets: I will have to prove that I have sufficient funds for the stay. According to the embassy and UDIs website, the required amount is 500Nok per day... so if i'm planning to stay +80 days, it will be something like +40.000nok. It is really hard for me to reach that amount of money at the moment of arriving, and I'm sure that I won't need that amount because I will be provided of accommodation by the host institute. Despite of that I wont be able to get a 'Guarantee declaration' from the hosts.
I was considering to declare a 45day tourist visit and later ask for an extension, in order to reduce the amounts that i'll have to prove, but I got confused when I read that I would also need to show my return tickets when entering to norway.
So basically, i would like to know if anyone had/know a similar experience in norway and what do they suggest to me. I dont know how important are these requirements in norway for these kind of visits.
Thanks for reading all of my post and excuse my english. I have a lot to practice before my (probable )trip.
Greetings