Indeed there is.
Tempted to just say that, but I'll go further. Money is intended to be earned normally until it's infinite. In the beginning, doing dungeons and exploring will be your best source of funds (selling items). Once you've traded enough to earn a mid-level merchant title, you'll be saving enough money buying potions that you can instantly sell them back to Martin for a profit.
So there are two fighting paths. You can either do guild quests, or you can explore (the compass icon). Exploring is the only way to find dungeons. The game does a random check every morning that you are exploring to see if you found a dungeon, and every time you don't find one, your percentage chance goes up.
Once you've found a dungeon, the game records the date, and you can enter that dungeon on that date (+ or - 5 days) in future lives.
