Manabarbs is a red ability, and damage is a lot fairer than life loss.
This is definitely waaaaaay too cheap.
I had thought that the legendary supertype would offset the cost, he is cheap enough to get into play early enough for it to matter against control, against aggro he'd probably not matter or be removed, and against combo he'd only be good against something like Deathlong which is paying tons of life in order to win. I could see a cost of 1BB, but anything more than that makes the card nearly unplayable unless the legendary supertype was removed. 2BB for the same card sans legendary supertype would be fine.
I don't want it to be a beatstick, I want it to be something which can slip under counters, punish control and place an even greater premium on artifact mana, and give black a creature it can actually run. Thanks to Onslaught and Mirrodin block the black creaturebase is dumpster worthy, the colour has been relegated to discard and tutor effects with the occasional creature removal spell. That pretty much sucks.