airport train to Oslo hotel

We (two adults and one student) will be staying at Oslo Best Western Bondeheimen Hotel (Rosenkrantz Gate).

What is the best and cheapest way to get to our hotel from the main airport? What is the closest station?
Do we have to take another means of transportation from there? Would transportation by taxi be much more expensive? Is there a possibility of getting a return ticket, which we would use to get to the airport for our flight back?

Thanks a lot.

Since "best" and "cheapest" are rarely the same I would suggest that you look up what you prefer:
The hotels directions (they recommend the bus -stop right next - stop: prof.Ascheoug plass):
http://book.bestwestern.com/bestwestern/propertyMapWeather.do?propertyCode=73038&group=false&disablenav=false&hideProgressBar=false
and as usualt the airports hopmepage has all details on all reatistic types of transport:
http://www.osl.no/osl/transportogparkering/10_Buss%2C<i>tog%2C+bil+og</i>taxi

Thanks a lot for your help :)

We took a look at airport Website and coudn't quite figure out the express bus fare (adult and student) from the airport to Prof. Ascheoug Plass in Oslo.
Do we have to take Fybussekspressen or Nor-way Busseskspress? Is there a possibility of getting a return ticket (to be used to travel to the airport to catch our flight back home)?

The fares: http://www.flybussen.no/oslo/index.asp?menuid=2617
(Single NOK 140, return NOK 240, Student (maybe only at Norwegian University): NOK 75).

Thank you very much for your help.