When was last rebuild? Says top end is fresh, how many hours on engine bottom? That doesn’t seem like a lot of money for a sorted kart. It’s a bit older but not important assuming frame isn’t bent or deeply worn down. (Check rails from below). I will not opine further on value because I am not knowledgeable about shifter karts.
Also, this for autocross? So parking lot track yes? There was a fellow on here doing the same thing, also with a shifter. Sounds like he was enjoying it a lot but challenge was getting tires to temp.