Is it hardwired or battery powered?
The value really depends on if the original owner signed up for a mylaps account, since you can't re-set the account for the transponder anymore. AMB has really locked up a monopoly to screw people over on these. If an account was never set-up, or the new buyer doesn't care about having one, you can get $350 or so all day for it (and really quickly). If the person wants to open an account and the transponder has already had an account linked to it, you can only get what AMB will give for "trade in" value on new one, which is about $150 (I think).
Check NASA Forums or Racing Junk to get some ideas. There's probably more than one "want to buy" ad for them on there already.
