My first question would be, is there any chance you have access to a Mill, if you do and can do a cad/cam files for the parts you need it should not that bad. If you have to buy the part, i could only guess, it depends oh how big the bank is you are doing to break. sorry thats not much help.
I will be adding ad 4th servro for index to mine in the next few months, I will be using it for engraving wine glass and some engraving on "round" pieces.