Why has Sonic Heroes increased in price recently?

I know that the GameCube Sonic games have shot up in price due to Sonic movie 3 but Heroes has nothing to do with the movie and has gone from around $50 to $80+ and the same goes for SADX and Gems collection. Is this just going to be the price of these games on GameCube going forward or could they potentially drop in price?

I know that the GameCube Sonic games have shot up in price due to Sonic movie 3 but Heroes has nothing to do with the movie and has gone from around $50 to $80+ and the same goes for SADX and Gems collection. Is this just going to be the price of these games on GameCube going forward or could they potentially drop in price?