Where to stay?
Oslo is one of the most expensive cities in the world. Misertravel recommends using the map view function and stay at a hotel walking distance to Oslo Central Train station. The airport express train stop here and is your best option to get to the city from the airport. https://flytoget.no/en/.
You have to book early to find a hotel in the 49 to 80 Euro per night range in Oslo. You will see there are not that many available for such a big city in that price range.
Misertravel stays at an amazing hotel walking distance from central station for 56 Euros per night. Check multiple booking sites since the prices can be different based on room type and if breakfast is included.
What to See?
Misertravel has toured all of Oslo and, the hop on and hop off bus tour is your best bargain here to get a great overview of Oslo. The tour bus takes you to many areas not easily accessible by public transportation and Oslo is a big city.