About $12 if I remember correctly.
I used it on Hyper wheels, and yeah it tinted the cores. If you also have Hypers or maybe any type of plastic core, mask them with something like ice cream tub plastic and hot glue around the edge, if you can. Just something to prevent the liquid getting in.
Mix 1/4 of the bottle of dye with warm water, then let the wheels soak overnight.
To put a design on the wheel, use wood or craft glue.