I've never seen one of those made of plastic...heck, the metal and glass ones cost about $4! That's plenty cheap enough for me.
My one gripe about much lighting- and not limited to the cheap kind- is that they are too closely sized to the A-19 bulb. This dissapoints me, as all but the smallest compact flourescents are considerably longer- and won't fit. (I'd rather spend my lighting money on light, rather than heat!)
