Currency in the Slayers world pretty much follows the common fantasy standard.
Most nations in the Slayers world accept gold and silver coins. Gold coins appear to be the currency of the better off such as nobility and adventurers, while silver coins are more regularly used by the common person. The Leeb (a coin from Atlas City) is worth 1/10th of a gold coin. Castles can cost millions of gold, while a really good 'deal' was a silver coin all you can eat buffet. Lina offered Gourry 500 silver for a sword, which he notes is the cost of buying a regular sword.
Lina shows that you can carry antiques or rare items for trade, like the antiquated coins worth more than the metal they are made of, or the orihalcon statue. Magic items and materials, while even more rare, are also part of the economy, as she was also able to sell a wardstone she made quite easily.