there is no price on something like this, except what you are willing to pay for it.
its not original, so the high priced rivet-counter range is out.
it seems to be mostly there, so the lower basket-case price is out too,
where does that fall in the middle? i dont know anything about preunits,
it seems to me that the machine is worth two or three thousand dollars, depending on what you abnd the seller are willing to negotiate.
a lot depends on what you want to do. do you want to make it a perfect restoration? lots of money there, so less of an offering price for a machine missing parts, like th eside covers and headlight nacelle.
do you want to ride it right away? ignore missing original things and ride it around.
you wont get a tight price range on anything this old.