OK, this is just one guy's opinion, so take this with a grain of salt, but I wouldn't work too hard making a solo tarp. The reason is that several folks make tarps with Cuben and it will be hard to differentiate yours. It might be possible that you will make your tarp significantly cheaper, or that you might make it in just the right size for someone, but that is about it.
Now, tents, on the other hand, are a completely different story. There are so many variations on tents, that if you make something different, you can charge almost whatever you feel like. For example, I know there are a lot of folks (myself included) that would love to buy a Contrail made from Cuben Fiber and Nanoseeum netting. This is assuming, of course, that the tent saves several ounces over the silnylon version (several being 4 or more in my opinion). How much would people pay? My guess is folks would be happy with $400, but still pay at $500. There are lots of inferior tents (in my opinion) at similar prices.
Another thing I would love is the X-Rocket in Cuben/Nanoseeum. This is my favorite design for a tent. Again, I'm not sure how much weight would be saved by switching to Cuben, but if it was significant, you could sell it just fine (at almost any price). In both cases, it wouldn't hurt to pencil it out and then ask us again. In the case of the X-Rocket, you could even make it go with someone else's poncho tarp (such as MLD).
In both of these cases, you are messing around with existing designs. It wouldn't hurt to tell these folks what you are doing. Of course, tent designs aren't necessarily rocket science -- I'm sure a lot of tents have simultaneous inventors. Nonetheless, if you created tents like either of these, I would give these folks a heads up.