There are very few things on a boat that are quick, easy and cheap but this may just be one of them.
We went to the local tyre merchant or scrappy, and got a slice of inner tube from a truck tyre. Cut to size with a stanley knife and squeeze it round the mast. It's surprisingly stretchy stuff. Once the mast is in the boat, drag the gaiter down and secure to mast and coachroof with big jubilee clips. It's lasted two seasons now with no sign of any deteriation.
Materials free, fitting ten minutes. Now if only everything was like that.....