Officeworks Yarraville has the b.box 450ml drink bottles on clearance for just $5, pretty great deal considering these usually go for $10 to 15.
Personally, I reckon these are one of the better kids drink bottles out there. Flip-top lid, built-in straw, easy for little hands to use, and most importantly, actually leak-proof (from my experience anyway). BPA-free and dishwasher safe too.