I’m not sure if you have one already or not, but coversandall.com makes great covers! And custom made, so you could send them measurements for what you are looking for. I don’t know what the cost of the cover you are looking at, but coversandall are usually around $70. I have three of these, and my dad has two. They are really good and hold up, being sunbrella material/fabric.
Just a thought.