Brad, How much?
Given how much trouble the old ones were at the race, I don’t think I would mess with buying a used one anywhere. Wouldn’t trust the battery. Besides, they still go for over $200 on eBay and the extra money for a new one is cheap insurance that your laps will count.
I asked the question before if you could use the same transponder for 2 different classes and the answer was yes. Is this still true as long as they do not run together?