True you can do it cheaper, but my personal opinion is, go for the optipac. You're buying a solution you KNOW works, and you now have an interface for a spinner, or even 2 spinners, and one more trackball if you wanted to.
Note: If you get an optipac, and you don't have an Ipac, get the Optipac USB version. It draws its power from the USB port Otherwise you have to get +5 and gnd to the optipac another way.
--NipsMG