Kit new cost about $400 lets say, the value here I think is in that trek mountain bike because theyre not cheap. The kit looks like it has at least been used half of its life so to me Id put a fair value $300 to $350, Id need to check on the value of the bike though to be more accurate.
However I got 210mph on a recent 300 mile trip so that may be possible depending on weight, tire pressure, and jettiing. My tires were 10lb over max and jet was set for grey plugs (not recommended) but not white and I carried a spare piston and cyclinder.
As far as $1000 that may be a bargain considering what some of the builders in my area charge. And look at what mopeds cost. IMO he's not that far off.