Hi Allan -
Australia Post has a flat rate envelope for $6, but its A4 sized and the weight limit is only 250g... say about a half pound. The next bracket is 250-500g which is probably where
T1-4 would sit, for $10.80 not including any packaging - if I was sending that module I'd probably put it in a postpak envelope with some cardboard, which would be another $1.65 or so. Add a couple of bucks for handling and that would be close to $15.
Don't know about insurance, but it sounds right. I never bother with it as it seems way out of proportion cost-wise.
Regards
Mike