Size 7 (standard chunky) zipper from Spotlight is available in black, white, navy and cream for (I think) $1.99p/m.
If you buy a zip around pencil case from Neds it costs you $4 and you have to do a bit of unpicking (but they use a very long stitch length, so it's very quick) but you get 2.5metres AND it's in pretty colours.
You only get 2 zipper pulls per pencil case, but they have rainbow ones with lots of short zips for $3 and you get about a dozen pulls from each of them.
Be not afraid of the zips, people. They can be your friends.
Except the ones with the metal teeth. They chip your fingernails.