Sir Hammerlock's Big Game Hunt is tallying-ho to Borderlands 2 today for Xbox 360, PlayStation 3, and PC. It's already reached XBLM, and will make its way to PlayStation Network and Steam later today. The third of the four announced DLC campaigns is free for Season Pass holders, but otherwise sets you back 800 MSP on XBLM, or $9.99 on PSN and Steam. If you're getting Big Game Hunt on PSN in Europe or Oceania, you'll have to wait one more day as it's scheduled there for tomorrow, Jan. 16.
As for when the fourth DLC campaign is due, Gearbox is still sticking to the 'by June 2013' line. That's despite the first three arriving within three months of the game's release, and there being a further five months until June. Ergo, the key word there is by.