I've played arena twice and went 3-3 on the first go and 6-3 on the 2nd.
On the 3-3 result I got:
45 dust + 1 pack
On the 6-3 result I got:
95g, 45 dust, 1 pack
Honestly, for a 150g entry fee, I feel that the arena is well priced. Even a mediocre 3-3 result nets you a pack + dust.