Yeah, that "observatory" is a rip-off of epic proportions, and not managed the way the NPS does most parks/monuments. There's no fee to enter the national monument proper (or a minimal one - I can't recall precisely), but to walk in to the observatory - which is really a gift shop and restrooms - they pop you with a $6 or $8 per person charge. Do they have a system for making you aware before you enter? No - they just yell at you when you walk through the door.
The ranger finally relented when we explained that we just wanted our daughter to be able to use the restroom and then we'd leave. I walked out to the plaza to wait, and in 5 minutes' time I was approached twice by other rangers pointing out that I didn't have a wristband and that I couldn't stand there and admire St. Helen's without it. I was boiling by the time we left and headed for our trailhead (no charge, thank you very much).
My trip was a helluva lot more pleasant in 1989. I was in awe of all of the fallen trees. Wow.
Yes, I agree, the observatory isn't exactly an observatory if they run it like that.
"Pay paradise...put up a parking lot...er I mean observatory."
