Value varies widely. A Late Model Series III with Hi/Lo transmission will bring the most money.
Most Series 1 I see are in the $2000-3000 range
Series II are $3000-6000
Series III are $4000-7000 with a few that have gone double that.
With no idea what it looks like, it is hard to give a value.
Parts are accessible for the engine and transmission to a degree. A few transmission items are no longer available. Body tin was exclusive to the series, however the rear fenders can use modified D14/D15 ones.
Right now they seem to be a good collectible since only a few thousand were made.