Is there a dedicated AF Assist device? (+Radio trigger okay)

I'm looking for something that's very small, rather cheap, and can give me AF assist when I don't want a huge brick of a flash hanging above the camera.

Is there any product available that provides dedicated AF assist only (a radio trigger is also fine too; I'm willing to switch)?

I know the RF-602s can wake up a flash remotely from standby when the meter is active. This could be tied into a sort-of AF assist, given supporting electronics on the transmitter, but it's on all of the time the metering is active, instead of just when the camera is focusing, so this method is suboptimal.

Is there any commercial solution that does a better job than this and doesn't cost $$$? (A 220EX - which goes for $50-60) comes to mind, but it's not "compact" anymore...)

I assume the ST-E2 is out of your price range. I'm finding it a lot more handy and useful than I thought when I bought it.