Are there 3, 4, 5, 6 thousand dollar mini bikes out there? Yes.
Are there that many people willing to pay that much for one? No.
If you want to ask and get "end of the rainbow" prices, you need to find the "end of the rainbow" buyer. The hard part is getting the very specific item and the very specific buyer to cross paths, and at the right time, and even then the stars need to align for it to all work out.
I have a buddy that recently paid $3500+ for a very rare, very desirable mini bike. The bike, the selling price, and the buyer were all critical parts of the sale happening. They somehow all found each other, and it somehow all worked out.