I've had some experience with the Citizen Tokyo. That model fits your budget.
Not sure of it's long term reliability/performance. Only had mine for a few months.

My first encounter w/ Tokyo's was when I visited my brother in California; he has
3 of them for the use of his big family. Borrowed one and taught it was okay for
what it cost. Even did some off road riding with it:
https://www.youtube.com/watch?v=XUUC...6zPoymgKaIoDLA

On one overseas trip; Jetblue wouldn't let me check in my Brompton in a cardboard box.
Bought a used Tokyo and squeezed it in my luggage. Rode it around for a few days and
the bike was okay. Sold it afterwards since I was moving and didn't have room for a 3rd bike:
https://www.youtube.com/watch?v=FR2T...6zPoymgKaIoDLA
2013 Citizen Tokyo in a suitcase by 1nterceptor, on Flickr