Scrolls
Mages (and to a lesser extent Priests) are prized as scroll-users. Even the meekest of spellcasters can become portable artillery when girded with half a dozen Thunderwave scrolls. A first-level scroll can be purchased for 25 gp or sold for half that amount.
Adventurers proficient in Elven can purchase scrolls at the discounted price of 20 gp.