I've seen small vises with the center bar threaded on both ends, then
larger rod segements tapped axially about half-way through for that
thread and screwed on. The rod segments are usually about as long as
they are wide, they don't look too bad. Bevel the ends slightly to
remove sharp edges. Larger vises sometimes have leather washers at
the handle ends, keeps the noise down when the bar slides through.
I've used rubber o-rings for the same purpose on the smaller vises, you
can also slide them along to keep the bar centered, if desired. For
cheap and cheesy, you could use a long bolt and turn the hex head down
to a cylinder.

Stan