Some of the simpler 406 wheel Bike Fridays will be a bit under 4 figures.
they have a hinge pivot behind the BB, and QR lever at the top.
so rear will fold,
seat mast will come down, fold forward..
There is, an alternate folding handle bar mast available now,
for the 20" wheel bikes.
I have one on my Pocket Llama, works nicely..
because of the pivot behind the BB, and the fold around it,
an IG hub needs a chain tensioner.
But you can get one set up with an IG hub.
or as a single speed at first, perhaps, an IG hub wheel build later..