Arena? What is the Arena?

[NTJedi]

ologm said:
You also get +150 experience. Free heroic ability early in the game.

As I wrote earlier... even if your commander is lucky enough to win he will most likely be cursed, horror marks, cursed items, blind or something else when playing against human players... thus not that useful! If you're talking super early in the game then it's still usually not worth sending someone if there's lots of human players. Lets not forget the prize will curse the winner to return to all future death matches as well.
And if you're playing a SP game then unless you have less than 4 computer opponents your chances of winning are very slim and thus NOT worth the life of a good commander.

Current prize value is only worth sending someone if it's a small number of opponents.