Primal Mana is used for lots of crafting recipes and enchants in TBC Classic. Arcane Resistance gear, Healing and Spell Power Enchants and even some good BoE epics, like the Netherstrike Set. It typically sells between 15 and 30 gold, depending on the economy on your server.
Farming Elemental Earth for gold at low levels
Elemental Earth is used primarily by Alchemists to make several kinds of potions. These Potions are much needed for Raids, which is why a single Elemental earth can sell for several gold. On my Server, I regularly sell my farmed Elemental Earth for 2g, and it sell very well at that price.