Hearthpwn

This is just a cheap Druid deck built to ramp up to big beefy minions.  A fairly good match up against all the aggro decks which are very common the current meta.  Black Knight or any other 'destroy a minion' type cards may take out a big tank but you can just lay down another.

Negatives: (1) You lack good card draw.  Not a *huge* deal as you should be playing your minions conservatively. Ancient of Lore helps a lot but this deck is supposed to be cheap.  (2) You don't have a finishing combo.  Your win condition (especially against aggro) is to simply survive until late game and then beat them to death with your beefy minions after they have exhausted themselves.

Mulligans: 1st priority is Innervate and Wild Growth--keep all of these.  If neither of Innervate nor Wild Growth is available then hang on to a 3 or 2 drop minion if possible (if you keep a 2/3 drop and have a Mark of the Wild, keep that as well). I throw everything else away. Your hero power can be used effectively early on if you get horribly unlucky.

Strategy: Early game plan your next two moves so you act in a mana efficient manner.   Make use of the Coin and Innervate to play your Wild Growths early if possible. If you suspect the opponent is running an aggro deck and you can Innervate out a 5/6 drop Taunt on turn 1/2 do that to mess up their early game.  Against Hunters I usually keep only one minion on the board unless my health gets below half, then I try to have two taunts up.  Against Warlock Aggro I try to keep two minions up and effectively use Swipe/Starfall/Wrath/Keeper of the Grove effectively.  Other decks: No specific advice, just trade effectively.  This budget deck will be facing an uphill battle against more expensive control decks.  This deck is not designed to get you all the way to legendary.

If you have the dust, make something like Dreadmaker's Ramp druid instead: http://www.hearthpwn.com/decks/42772-dreadmakers-ramp-druid

Thanks!