Like the person above me said, g.e value won't go much beyond 50k, but the street price will varry, They usualy go up the time of a big item dump for obvious reasons, i think they'l stay around 3-4m for now though, untill maybe phats get dumped or something.
Mint cakes will just rise until eventually they get dumped by the rich players. They aren't actually worth anything unless you've got tons of junk (meaning you obviously lost money in the past) so the whole junk trading thing is ridiculous.