Assuming you want to spend the time planning, I think your money is better spent on getting everyone a few key tokens for their class, rather than 10 packs. Making sure the sliding classes have a melee and ranged weapon.
Let's say I'm a new Fighter. Instead of getting a random 10-pack for $6, I'd get the following for about $6 total:
+1 Thrall Sword (Rare)
Sling of Seeking (Uncommon)
Thrall Lieutenant Armor (Uncommon)
Thrall Large Shield (Uncommon)
Shirt of Brawn (Uncommon)
And maybe I'd splurge for another $2 and get Gauntlets of Ogre Power.
Then in the coaching room I'd hope for / try to trade for anything that gives HP, AC, Strength, melee hit/damage, or Saves. Some good commons that should not be difficult to get: Thrall Bracers, Thrall Belt, Thrall Helm.
That is a pretty solid start for not much money.
That all said, you can certainly come into TD with nothing and still have fun.
Classes Played: Barbarian (65 times), Monk (56), Ranger (33), Rogue (25), Cleric (21), Fighter (13), Druid (12), Paladin (11), Dwarf Fighter (10), Bard (7), Elf Wizard (2), Wizard (2)