Full covers are not common. Those who have them more commonly use them for long term winter storage. The sun doesn't beat down the hull as bad as the deck. Regular waxing with a marine wax will take care of that for you. A full boat canvas is going to be expensive. I think $750 is a good price.
As the owner of an upholstery shop, I can tell you that $750 is a decent price, as long as the workmanship is quality and they're using UV thread. Sunbrella, Dickson Marine, Seaquest, etc canvas isn't cheap.
I looked at a full boat cover last fall here in MN. It was about $900 for 23' runabout. I did some research and found that the better custom covers were worth the money, as they would not abrade hull in windy conditions. I can give you the name of a good shop here, but I can't imagine you can't find one locally.
