I'm just curious what you plan n using for a pinball? A standard steel bearing would destroy that - very likely on the first whack - or at least break an end off. If it's more for a "toy" pinball you'll be fine. I've been thinking of designing some popper bumpers, slingshots and flippers myself.

Autodesk offer a 3D printing service if you use their free 3D design package Autodesk 123D http://www.123dapp.com/123d

I've no idea what their prices are like, I've never used the service. Has anyone here use autodesk or some other 3D printing service?