What's wrong with a (PMDC) ESC? Preferably voltage programmable. That's just a buck converter with voltage regulation (and presumably soft startacceleration and torque controlprogrammable current limiting), possibly ready-to-go.
You can get a buck converter for that level, but it'll be pretty beefy (or, those junk modules, pretty sketch), or a bit tricky to make from scratch.
Like, I have a few things on hand that can do that, but, they're not exactly products, and it's not economical for me to try and sell them, sadly.
Tim