What's the asking price? I'd agree on maxing out around 60$; if you plan to put it together yourself, you may put more into it than it'll be worth but the parts are pretty common and fit many models so they can be had pretty cheaply. Or you could probably find a nearly whole bike lest the tank for 75-100$ and make one nice, complete bike. Or build it up the way you want with parts you have lying around!
Make sure all of the light parts are there, lens, battery tray, dashboard switch. Those are the hardest parts to find on these space race bikes and the ones that would cost the most to complete it. Good luck!