"The Grand Tourny is actually free, only costs 700 gold to buy each level"
This is completely incorrect. The Grand Tournament is not an adventure like Naxxramas or Blackrock Mountain (which do cost 700G per wing, or you can buy them for real money). It's an expansion that comes in booster packs of 5 cards that cost 100G each or can be bulk bought with real money.
You can play Hearthstone for free, but it's pretty painful unless you're already good at it. The best advice for new players is to save your gold for Arenas (which reward packs and cards and let you learn by experience) and buy Naxx and BRM for money. Basically it's now a $50 game with further optional micro-transactions. It's still good VFM at that level, though.
(Handy tip for people who plan to spend real money: if you have an Android device, install the Amazon app version of the game and make purchases through that using Amazon Coins. The coins are discounted at least 10% when bought in bulk, plus there's often a partial rebate on Coin purchases - IIRC there's a 25% rebate on right now in the US. Also you'll be given a free Classic booster pack the first time you complete a game on each of an Android tablet and phone, an iPad and an iPhone.)