The smarty isn't a chip, it's a programmer for your ECM that contains 10 different programs from economy to wild advance and duration for the injection timing.
I just bought a new one for $645 to my door fed-X.
I've seen one used one offered for $500.
Things to look for:
Damage from heat or cold (below 33F).
The units go into vin lock when any of their programs are loaded to the ECM, so the seller has to load his original program back to his truck ECM to unlock the unit. If it's locked it's worthless.
So as long as it isn't locked or damaged I would guess $500 or whatever lesser amount you can negotiate.
When a program is loaded it turns on high idle. when the original program is put back the high idle stays on.
I know, more info than you were looking for but thought I would tell you anyway.