Scored these today for $10 at a local 2nd hand store, 2 wheels with 2 covers per wheel, plus a spare cover, for a total of 5 (yet another thing to add to my list of things-I-don't-have-time-to-do-right-now
).
Apparently they're off a sulky (a kind of modern chariot), used for horse "harness racing". Diameter ~57cm, dish of about 45mm (not including the thicker ring at the centre where it screws on) - they'll need some trimming of course, so they might end up a little less dished, but should still be better than flat. Reasonably sturdy, impact resistant plastic (as you'd expect).
Similar covers seem to go for about $20 new (unless someone can find a cheaper source) so they're not that much cheaper than actual mooneyes - I don't expect they'll displace pizza pans any time soon, but they might be worth looking out for if anyone lives near somewhere they do harness racing.
I'm thinking with not
too much work they could be made to look a lot like those fancy yurastyle covers ... now all I have to do is find a nice non-destructive way to attach them to the pictured alloys. Using the original mounting screws would be a nice option, though I'd want to clean up the sharp edges near the centre a bit. Alternately the centre ring could be cut out and some sort of mounting ring attached to the wheel, with attachment around the edge...