At this point you have two choices: either get in and get the season pass (you'll have to buy Mecromancer and the extra), or wait a while for the GOTY version, which will probably have ALL the DLC bundled in (including the Mecromancer).
Honestly, for me the deciding factor is if your friends are playing it. If so, yeah it's fun because you'll have friends to play with. But if you're going to solo it, just wait.
If you didn't play BL1, go ahead and pick up the GOTY version, it's been on sale often.
Argentina, it was a while back, but the season pass was a free download for that region. Someone had posted on reddit that by doing the ole new gamertag and downloading via that one but playing on your main would allow access to the 4 DLC campaigns.
But like I said I'm not exactly sure if Gearbox or Microsoft has done something or found someway around people doing that.
GT: Social Sin Fanboys = The bane of any intelligent individual