The solar cover (the name is a misnomer) greatly reduces your cost by reducing evaporation. I leave mine on anytime I am not swimming.

As for quality, I have found it best to buy the cheapest you can find. While others may argue about this, here is my logic. If you are lucky a good cover will give you two years. They get ratty by year three. A cheapo one will give you one maybe two years. I bought my cheap 20 x 40 two years ago for $89. Most 20 x 40 go for $200 or more. You do the math. Plus the cheap thin ones are much easy to handle.