One amazing way to save money is using "Family Cultural Passes" from the Clackamas County Library http://www.lincc.lib.or.us/cp/cp-list.html It's free- all you need is a library card from Clackamas County. You reserve them in advance by calling your closest library . Currently ones are available
Japanese Garden
Museum of the Oregon Territory
Stevens-Crawford House
Oregon Garden
Pittock Mansion
Portland Art Museum
Portland Children's Museum 2nd Generation
Oregon Sports Hall of Fame
You can save a TON of money using these. Check out the link to the passes above for more information. I know the Portland Art museum alone is $10 for an adult last time I was there!