I would bite the bullet and get a new one. Firstly, its new. What happens if you buy an expensive adapter... and the scanner dies?
2nd.. I don't know the specs of the UMAX but you may end up with a better machine.. better bit depth/color/resolution. And the new one will have a warranty and you won't have to deal with the headache of trying to make it work.
If you want to get out as cheap as possible... I would hunt down another G4.
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