Could buy some plexi from the local home depot. You'll need a router to cut it into circles, or you'll have to know someone who can do it for you. Each wheel will probably cost you $15-$25 worth of plexiglass. Also it'll collect dust, dirt, brake dust and muddy water and will probably look horrible in no time flat. It'll look better than smooth wheel covers at first, but it'll probably quickly start to look worse.
I think black steele wheels actually look pretty neat without the hubcaps off, tho I am a bit weird. Maybe if you did the pizza pan mod but just painted it matte black it'd look good?