The Merlexi Craft Liberty series of wheelchairs are crafted from a reinforced polypropylene frame that makes them light and easy to move—29 pounds when in use and 19 pounds with the wheels and arm rests removed for portage. They even make an "MRI" variant that is usable around magnetic resonance imaging machines that includes no metal at all.
Prices are around a thousand dollars.
For a few years during my childhood my parents and I worked in a live-in group home for mentally retarded and/or ill people. (There is probably a better term than "retarded" in use these days, but as I no longer work in health care and am not very comfortable with some of the other ever-changing terms used to describe those being cared for—"clients," "consumers," "beds"—I'm just going with "retarded".) Hauling around wheelchairs was a major hassle—especially if you were sitting in one. I retain to this day a fascination with the tools that exist to assist the handicapped (another loaded term, I know). Sending me tips about this sort of equipment is definitely welcome. (Has anyone come up with a better version of those back-of-the-van chair lifts yet?)
Company Page [Merlexi.com] (Thanks, Matt!)