We are doing a backsplash for a black, honed granite countertop. White shaker cabinets. Gray grout. I would like white subway tiles, not polished.

I am not sure if we should purchase and then hire the local "big box" construction supply store and hire them to install, or go to our local flooring store. The flooring store appears to be upmarket......but I know nothing about tiling costs! Please help me out. Thank you.