While I can't recommend a particular canvas shop I will tell you that Sunbrella fabric, http://www.sunbrella.com/
,is an excellent choice of material. My current custom cover was produced in 2003 using Sunbrella and the fabric is as good as new, not to mention the boat is protected from the harsh outdoor conditions. Custom is the only way to go. Ensure the cover has an extra layer of herculite on the backside to prevent chaffing against metal and fiberglass components. As for price, talk them down and offer cash for a better deal. Small canvas shops love cash much more than credit and checks as I think it has something to do with Uncle Sam.