kinda hard to say. The kit seems to be discontinued. I can't find any of the major RC sites that are carrying it anymore although parts are plentiful. The kit retailed for $300 so if its RTR with decent electronics or its like new then Id say, it could be worth $250.
For some reason I didnt see the craigslist link at first. The kit looks like it in reasonable condition and if the Castle electronics are in good condition along with the handful of spares its a decent price. Id probably offer him $225 and see what he says.