We've got the powder too my DS recats to it tho for some reason which is why I usually use the cubes! But yep the powder probably works out cheaper.
Another thought I had on the snack / recess / afternoon tea front: I usually bake from scractch but those Greens carrot, date cake etc mixes are actually really good - they ahve no artificial colours or flavours and Coles quite often have them on special for $2 and I keep them in the pantry as a back up. I grate in some extra carrot and zucchini and toss in some sultanas and they are yummy, cheap and freeze well- you can freeze individual slices and thraw them out for recess etc and one cake would last the week. The pack includes icing as an option too.