I recently got a chance to look at the Six Moon Designs cuben Haven. The inner tent from a Coleman, Peak 1, Cobra fits nicely under it. A few minor modifications would make it work.
This is probably a match-up that very few would be interested in. The buyer of the 10 ounce, $400, SMD cuben tarp is probably looking for something different than the owner of a $69, Cobra with a 1.5 lb inner tent. But who knows?
The Haven/Cobra combo would weigh a little over 2 lbs for the tent+fly (excluding poles, stakes, etc.).