For a starter druid tank, I would say stay in Ramps, Mech and Coilfang heroics. Maybe BF and the first tanaris heroic (cant remember the name), but these are a litlle more dificult.
Ramps is easy. The only difficult part is the pull with 4 caster and 1 melee. You want to bring some CC for a starter pug, so mage/rogue/hunter are your friends here. Particularly mages. You can bring a spriest to MC too, maybe.
Mech is easy too. Not too much CC needed, but you will want a mage and maybe a hunter too, for the gauntlet. Things can get pretty messier there. A lock would be a third fine choice, for some banish on the demons.
Coilfang's heroic are needed so you can get rep to get the tank staff(Earthwarden).
SP is pretty easy and quick. You will likely need at least one mage/rogue/hunter though, for some CC. I would recommed you to read some strategies about that heroic, because there are several pulls you can just go through. The worst pull there is, probably, those after the second boss. Use extensive CC here, even your hibernation.
Underbog is longer, gives more badges and may wear a PUG off, and its a litlle trickier. You will need at least 2 CCs here for some pulls. I wont get in too much details here, its a really long heroic, so I recommend you to read some strategy.
SV, IMHO, is easy too. But, some ppl thinks its one of the hard heroics. You will need a mage/lock/hunter to do some AoE dmg and some kiting for the second boss (the mechanic one). One of them have to be focusing on the adds. Some ppl like to bring a lock for the first boss, so you banish one of the elementals, kill the other and focus on the boss, to get the elemental despawned when the boss is killed. I think its a valid strategy, and make things easier, but not really needed. The third and last boss is a wuss, once you know how to do it. You have to tank him by the side of one of those aquariums and once it becomed active, everyone has to dps the aquarium, even you. When the aquarium is destroyed, kite the boss till the next one. Aside that, its a tank/spank boss.
For what to spend in badges, I would say go for the idol, then ring and bracer or cape(depending what gives you better stats, choose one to go first), they are the best you can get.
I would say you buy from AH the Necklace of the Deep, the Belt of Natural Power and the famous druid trinket, Badge of Tenacity.
Get them gemmed/enchanted and you will be better.
Once you have Earthwarden (or if you get to meet the minimuns for kara without him), start OTing in Kara, so you can get better equipment and badges.
Oh, and this has to be stressed, read strats, talk with people who did those instances before so you learn the tricks on doing heroics, yada yada yada...
Good luck.