Something that is fairly easy to find or possibly upgrade components to? New or used doesn't matter. $1,000 or less target price range.
Check out the specs for a Downtube Mini with an Alfine 11sp on it. About $1000
https://downtube.com/downtube-minib-...-folding-bike/
I bought a used Dahon Curve D3 and upgraded to a Sturmey Archer X-RF8. I was able to do this for under $1000
Here is my thoughts and experiences.
http://www.bikeforums.net/folding-bi...8-120-old.html
http://www.bikeforums.net/folding-bi...tes-later.html