I'm under the impression its fairly simple to make a tarp on your own, with much less than 16 oz of weight! Campmor sells all sorts of cheap tarps as well, including a 6x8 9 oz silnylon for $70, or check out cheaper heavier tarps: http://www.campmor.com/gear/tents/tarps.shtml

One thing you might think about, if you know you'll be comfortable under a small tarp, is a poncho tarp.

I have a Sea to Summit Poncho nylon tarp that weighs 13 oz, but it's cheap ($30) and serves as both raingear and a shelter. That's about a 16-17 oz shelter system for $40 in relation to a 20 oz tent for $400, not counting the multi-purpose aspect.

I'm going to be getting rid of this poncho tarp in favor of the Golite Silnylon equivalent, which is 7 oz and $60.