You are correct there. 20" and lightweight do not work unless you're willing to spend MAJOR dollars.
Carson has a set of 20's on his, don't know the brand. Here's a pic...
I have a set of 20's too. They are KMC 820 SS and not made anymore. they mimick American Torque Thrusts and my wheel/tire combo is surprisingly just 12 pounds heavier then the OEM wheel/tire combination (our stock wheels are HEAVY!).