Not cheap, you have to find a place that can dip the entire chassis, unlike Soda blasting. Both have pros and cons. I believe there is a place up in Toronto that can do it. You have to strip it down to a bare shell, no fuel tank, wiring, absolutely nothing on it. Any removable body panel must be removed, all glass too. I’ve looked into it for the 951, honestly, you’re better off getting the car blasted.
Acid has a couple week lead time, and it has to be coated after it comes out or things start to rust pretty quickly.