It looks like it's about $12 on Amazon, but it's hard to be certain if it is this exact model.
There's two different sizes, small ones and large ones.
You can use whatever locker is available that you want.
Some PFs have code pads on the lockers, but most of them just have holes you can put your own lock on. The holes are standard padlock size. If you don't have a padlock, you don't HAVE to lock your locker, but if you get your stuff stolen, that's on you. And if you don't have a lock, you can buy them at the front desk where you entered. IMO, the best lock to buy is one with 3 or 4 numbers on rotating wheels, so you don't need a key on your person when you're working out, something like https://www.amazon.com/dp/B00FFZ1LPS/