You can still send a DVD case (game or movie) by using letter post here for less than $3aud, as long as it's only 1 disc and under a certain weight. Also thickness (can't remember what that is now). Then it bumps up to around $3.50 or something. Both of those are untracked.
The lowest amount... can't remember what it is now, but I think it's for letter under 5mm. It's less than $2aud (close to $1 iirc). People use that for sending like game manual only, or a couple of slim manuals.