Why are these lenses so cheap?

Nikon (Nikkor) 50mm 1.2 Lens
I see them for $65 bucks, to me this seems like an amazing deal?

That sounds like a scam. Check out the site where you're seeing this lens here.
http://www.resellerratings.com/

Nikon has made some variations of this lens, some of those in quite large numbers.So, they're not rare. Quite a few of these will need a hardware modifcation before they can be used on todays cameras. Additionally they are of an age that fungus can play a role.

So…
not rare
possibly in bad condition
may need modification

That adds up to the fact that you sometimes can find a useable 50mm f1.2 for less than a 100 dollars, do be sure to read the small print or ask about the condition

F/1.2 lenses won't go lower than three digits unless it's a TV lens.