I'd be fine with anything as long as it's well built and interesting
Have you heard of Autodromo? They're quite a new brand but their products are all based on motorsports and cars (hence the name).
The Autodromo Stradale is just slightly above your budget at $875 but it is automatic, well built, and interesting.
For $600 it's going to be really really hard to get something like a Rolex, Breitling, Omega, etc no matter the age or condition.