Bergen to Oslo then where?

Check Norway in a Nutshell and they have a number of transportation options from Oslo to Bergen or reverse from Bergen to Oslo. You can take a ferry boat to a special train that'll take you to another train which will take you into Oslo. It's about 310 miles between Bergen and Oslo, so it makes for a long day of travel.

We have reservations between Copenhagen and Oslo on Norwegian Air Shuttle for $71.

You don't say when you're wanting to go to Scandinavia. I suggest you look the cities up on Wikipedia and see the average temperatures, etc. September is an especially wet month for many cities--with 20 days rain in many places.

See more about the Norway in a Nutshell at http://www.norwaynutshell.com/en/explore-the-fjords/norway-in-a-nutshell/.

Both Copenhagen and Stockholm can be expensive, if you don't watch your spending. But in either city, the main price that matters is the one hotel room, B&B or hostel that you actually reserve. Once you've don't that, you know the price and can budget around it.

The Oslo Folk Museum (and the other Bygdøy museums/attractions) may appeal to your architecture background.
http://www.norskfolkemuseum.no/en/

http://www.visitoslo.com/en/activities-and-attractions/boroughs/bygdoy/

Bus 30 runs year round but the seasonal ferry is a must at least one way. Oslo card covers both museums and transportation.
http://www.visitoslo.com/en/activities-and-attractions/oslo-pass/

Drive from Oslo to Stromstad, Sweden to enjoy the archipelago all the way down to Goteborg. The islands and villages are scenic and inviting during the Summer months. A boat or ferry is necessary.