I looked at the things you did within 3 days and must admit that's quite a bit!
Mt. St. Helens is a huge place. It would take a couple of days to trek up to the viewing pts let alone going up to the rim (which is not allowed anyways). As for the Sea Lion's cave and the Catholic church, I find them too 'tourist' and can't stand going with a group.
I never went with a tour group as I like to have my own pace. I am a bit surprise the tour does not have the columbia gorge in it...it's such a spectacular site.
Maybe I am getting old now...I don't buy much at these shopping outlets anymore so I don't worry about taxes....and I rather pay taxes (using my Nexus) than trying to cheat them over $50 bucks....just my thought.