There are plenty of cheap ab rollers on the market for core training. The Rogue Bumper Ab Roller lets you use your favorite weight plate as an ab roller. It supports bumper plates from 10lb to 45lb and has internal ball bearings for smooth movement on the ground.
The Rogue Bumper Ab Roller comes with non-slip rubber handles. It works with plates with a center hub diameter of 50mm. Sets you back $40 at this time.