I'm not sure how you'd heat them all. Do you heat the room or keep them in a shallow heated tank?
I'm starting to collect the 85c homebrand soft drink bottles, got about four so far but I can get more if the need arises.
Do you have a Plastic Box, plastics place or wholesale food factory in Wellington?
I went into Plastic Box the other day and they had 50 700ml disposable food containers like the ones you get from Thai and Chinese resturants for $6 and 50lids for $6 too I think.