I got mine at national discount covers 5 years ago. I bought the cheap one and it has been quite good I'll have to say. The first year I cinched it down tying all the loops going under the body and it did some tearing at the corners.
After that I only tie one down under the middle, then I go around the entire base of the motor home with a long rope right above the bumpers. This takes care of the billowing and has worked really well the last 4 years.
I don't think it's the price as much as it is the installation method used.
Brian