I made a helm (cockpit cover) last year for MyOtherBoat) Materials were about $200 and add to that some decent snap tooling ( vice grip type, about 50 bucks or so.
I have an industrial sewing machine and that helps a lot. There is a good how to video on the Sailrite web site. The key to a good job is to use the patterning material and double sided tape recommended and make a well fitted pattern.
I used a less expensive material than Sunbrella since this was my first helm cover project. It is a fairly light material and you could probably sew it with a decent home machine. A lot depends on the thickness of the edge banding.
If you go this route take my advice to install and carefully remove your canvas enclosure so that all the movable snaps are in the correct position before marking and installing the snaps in the new cover. Don't ask me how I learned that