Since gold is somewhat rare in the game, this may seem like a daunting task. But there are several ways to get money that will help make this easier:
1. Sell old equipment. Keep in mind that if you plan on playing Millenium 2, your inventory does carry over as well. You may want to be mindful of what you're selling, but outdated equipment can be sold for a decent price.
2. There are two enemies in the Rocky Path that drop items worth a lot of money: the Golem and the Bird enemies. The Golems drop Precious Nuggets and the Birds will drop Feathers.
3. There is a woman in Festina who will buy items for a much higher price than other merchants. She is the woman in the north-western corner who will complain that the woman at the stall next to her is getting more business.
4. Wear the Noble Ring when going to sell items. Equipping this on Marine will allow you to sell items for a much higher price.
5. Finally, the Metal Guardian enemies that you fight in the Ancient Temple will give you 500 gold per Metal Guardian you fight in an encounter. While going through the temple, you will fight many of them naturally.