Update: Is this the Batmobile Newton? Maybe. Bidding has pushed it up over $400.
If you are quick (and Apple isn’t reading this) you can pick up a piece of Apple history on eBay right now. Someone is selling a prototype Newton MessagePAD Prototype DVT Unit. From the description:
Differences between this unit and the final version is the labeling “Notepad” on the front (instead of Messagepad), it lacks “Newton” labeling at the top of the device, and on the back side there are stickers showing that this unit is not FCC approved.
It also appears to boot the Newton OS 1.3 as well.