It's basically whatever the market will bare/bear. Or how bad do you want one? After that, the normal devaluation depends on condition (all aspects of that), and average 'market' price.
That's absolutely no help, is it? I know what I paid for a new one, I won't get within 1/2 that for a used one. Then again, I wasn't happy with it (my probelm, not the radio's, it worked as specified).
- 'Doc