Received 600 feathers for a dragon kill. You can get comparable feather rewards in a single group killing a couple of lower bosses in some dungeons. The difficulty and coordination required for a dragon kill is a lot. I would think 2500-3000 feathers perhaps would be more reasonable (it should be divisible by 15000 - typical item cost). That compares to probably 8,000 feathers for epic dungeon raid (but that tends to take a bit longer to do).