If you are going to return the core then go with the lowest cost one that offers lifetime warranty. PS Pumps on a 4cyl are pretty easy to change with just 3 bolts and 1 belt to remove.
If not returning the core, I'd say go with the new Cardone with a Lifetime Warranty.
That $255 is for a whole reman pump. Not an actual rebuild kit. Unfortunately, you can't get every single internal part individually, but maybe he can get the culprit bearing?
EDIT: By the way, pull the pulley with the pump on the car. Put a screwdriver through to hold it. You'll thank me later. Haha!