Should i sell my nikon fisheye that i got for about 50% off?

So the nikon fisheye i got (16mm) is ussually around 800 but i bought it in a new conditiion from ebay for about 350. Its still pretty new.

I don't use much because i have a d3100 that doesn't have the focus motor. I wanted to save up for a d7000 and then sell my d3100 and buy some lighting. I was thinking i could sell the fisheye for a bit more than i paid for it but then i don't know if ill ever find a deal like that again.people were selling the same fisheye for 500 and it wasn't new and come had cracks.

Should i just be patient and save up?

Added (1). I do use it but not as much as i want because i have to manually focus it. The main reason i want to get the d7000 is to use it more

I'd probably sell it. Keeping something of value that you won't use gains you nothing.
No doubt, a Nikon fish-eye is a fine lens. But if you don't use it, what good is it?

Don't be scared to focus manually. The fisheye is a superwide lens that hardly needs focusing at all. Don't sell. Enjoy it instead. Set it f/16 for focus-free shooting. Move the focus ring so that infinity falls above the small 16 number on the left of the DOF scale. You should now get everything clear from the tip of your nose to infinity with having to bother about focusing at all.

BTW, it's already worth $900 brand new.