I would go with a product certified by the manufacturer. Here is a link to Sunbrella's cleanning and care page:
We're talking between $12-$20 for a bottle and it only needs to be done once per year. I understand the economy is the way it is, and more money/less cost is always good. It is my understanding that you need to be careful what products you use on sunbrella. I would hate to cause damage or prematurely shorten the lifespan of a product by trying to save a dollar or two.
Just my humble opinion.