I couldn't find any cuben fiber on eBay, but I did find SilNylon for under $8/yard. So I got 4 yards of it, it's 65" wide, and I'm going to make a simple 8x5 tarp mainly for use as a "vestibule" on our BD Lighthouse. Since this is my first time doing anything like this, I tried to get a feel for what the finished tarp would look like, and I was all like WOW THAT'S BIG.
It was heat cut but I suppose I'll need to make seams and tie-outs anyway. My boyfriend's mother has a 20-year-old sewing machine that I'll brush up on before attacking this, at any rate, and then I'll probably use the rest to make a daypack. I still can't believe how thin and light it is.