if you have an animates near you just ask them if you can have the polystyrene boxes their fish come in. Also I know that the $2 shop (or similar) has had heat pads, at least in christchurch. You just remove them from their pack and contact with air causes them to heat up, they last for about 15-20 hours, so that should give you plenty of time. These pads are similar to the ones that fish are shipped with originally. Hope this helps .