That one I linked was, IIRC, 7075 aluminum, not steel. (and on closeout for $10 if you can't find a used one for free)
A nice crankset (2 arms, two chainrings, and bolts) weighs about a pound and a half. The smaller (42 tooth) chainring alone probably weighs less than 3 ounces. I was thinking you could screw the chainring to a 18" Mongo wheel, but maybe that wouldn't be feasible.
Ah, I didn't notice the link. It's all skeletonized and aluminum. That would work great.
Ian