Hi,
I'm not on Vista now but was on Oceania in January.
There's no charge for the Aquamar Terrace but access is limited to 1.Concierge and above cabin passengers 2.Anyone having a spa treatment
Yes, the spa prices are very high on all cruise ships. I recall the massage prices being that bad. They usually offer specials on port days. Also, if you attend the Spa tour on the day you embark, they sometimes offer a package.
Hope this info helps. Enjoy 🌊🎉