Roller bearings can be had from Ingress Engineering in Canada for as little as $85 for a set of three. If you use only one of the two bearing cups at each location instead of two (look at them to understand what that means!), with the ball bearing directly in contact with the bottom of the component being isolated instead of the top cup, buy three more ball bearings and that set of three becomes two sets of three. Much cheaper than some other high end isolators, and not much more than Sorbothane half-spheres.
