Our primary school also does it through OfficeMax. I've found their prices are comparable with what you might get elsewhere. I've not found it cheaper to shop around except for the costlier items, eg, dictionary (usually cheaper at Big W), calculator, USB drives, art pencils.

Having said that, for the budget-minded, we keep our overflow supplies from each year and only buy those things that we absolutely need. For eg, each year they might say your child needs a dictionary - but in actual fact it's the same dictionary that only changes once from lower to upper primary AND you can usually get it cheaper at Big W. Every year, I sit down with a box of nappy wipes and clean and sharpen all the pencils, test out the textas etc. This usually means we only need to top up a few items rather than buying every single thing on the list. Likewise, any exercise books that only have a few of the pages used get re-covered and used the following year. You would be surprised how much you can save by doing this.

In early primary school they often share all the pencils etc in tins, so I send them in like normal, but in higher grades the spare stationery stays at home in MY cupboard, regardless of what the teacher says. Especially in public schools where the school cannot require the parents to supply stationery. In the past we've sent it all in as requested for the "spares" cupboard (eg multiple pens, pencils, coloring, gluesticks) but in actual fact those materials have been given to other students, so there were none left to replace DD's supplies as she ran out of things during the year.