We’re currently building and in the 4-5 quotes we got in the DFW area those prices are in line. We ended up going with a similar product to Hydrazzo, called Durazzo and it was a $4500 up charge. I had a bid for Primera Stone and it was a $5700 up charge. Both up charges over white plaster. The one builder that listed prices without a base charge came in at 8-9k for Pebble Sheen and $12k for a polished plaster (don’t remember which one but similar to Primera Stone)
I’d expect Hydrazzo to be a little more then Durazzo, but less then like a Primera Stone.
There’s several posts on this forum about other polished finishes - Hydrazzo, Durazzo, Primera Stone. Search those and you’ll get good advice. Polished surfaces are less susceptible to mottling if you do a lighter color, most complaints from discoloration come from darker colors and pool water management.
I think Primera Edge was my favorite, but they’re all good and matters more on the skill of your installer
Good luck!