I went cheap and easy, and am very happy with the results, which are functional if not pretty. Bought a 6'x 8' heavy
weight grey tarp ($10). On the long side, fold about 4" from the edge over a 1/4" nylon rope. Grey duct tape to hold the seam. Fold duct tape over each end of the rope where it protrudes from tarp and trim the rope to leave a tab which helps pull/thread the edge through the keder rail. A couple of adjustable poles ($15 at Canadian Tire) and some guy ropes and it's ready. I can thread it through the existing keder rail myself, but it's easier with an extra hand. I already had the poles, rope and duct tape, so my total cost was under $10. Happiness! Went with the small awning tarp because we are often in tight or uneven spots where a bigger awning wouldn't fit. This rig has withstood very heavy rain and high winds this
fall.