What you're looking for is called a Tudor Black Bay 58 ๐
Considering the submariner sells for $9100 and go well above that on the second hand market, it's not happening for 6k, not even vintage ones. Not to mention it's almost impossible to get one from an AD unless you have a spend record or wait possibly years for it
The closest thing you can find to a sub within your budget would be a vintage Tudor Submariner like THIS ONE for $5k, But be careful buying vintage. Parts could be swapped out / not original / broken / damaged, etc. Going vintage is not a good idea if you don't have extensive knowledge on what you're buying