One of the Jacks will probably post the sale soon.
My comment is that $36 is a good deal on a new, entry level tarp. No, it is not silnylon, it is polyurethane coated so it weighs 24 ounces.
The diagonal will be less than 12.5 feet, how much less, I do not know. On their silnylon 8x8s, the finished size was near 7.2 feet giving a 10' diagonal.