What are your interests and price range?
The Walker Art Museum is FREE every Thursday from 5:00 p.m. until closing (I think 9:00 p.m.).
Here in the TC metro, we are so blessed with so many museums, many of them are gems that most have never heard from. The St. Paul Libraries have museum passes that you can "check out", and give you free admission (either for 2 or for 4) to various museums.
Do you like live theater? Most of the smaller theaters have tickets in the $15-$20 range.
I've never done this, but I think it would be cool to have a "progressive" dinner at three different restaurants. Go to one restaurant for drinks and appetizer, and a second for the entree, and a third for dessert.