The mentality of those who willing to pay for Void charm is simple: OP Teleport skill will make doing most ubers easier than ever (Duncraig, Kabraxis, Unformed Land,...). And they will stick to a lazy ass style for the rest of ladder
My suggestion is to make The Void an actual "impossible" dungeon as it means to be. At this point the reward could give you OP shit stats (like Teleport atm) but wouldn't make any huge impact on playstyle, since you almost finished the game content.
Sorry for bad English.edit: Or you could, simply, nerf the charm.