The cheapest item to break down into materials (that are useful to a point) are regular ol' Potions. Takes 1 Alkahest to break down 1 Potion. Alkahests themselves cost 800g or drop off an enemy consistantly way later in the game. Farming money is a pain in the early game, so if you wanna be patient on this, wait to fight Amys. They also drop off another enemy but with less chance. So go to Johannes, and get breakin' em down. 10 of 'em and it's yours.