If you want to make or upgrade weapons and armor, you will need a lot of money in Monster Hutner Stories 2. That being said, you can make money really easily by gathering items from both monsters and item nodes and selling them.
You can gather monsters by defeating both small and big monsters in battles and then selling them back in a village by talking to a shop NPC. You can also gather what are called trade items, which are meant only to be sold at shops. Doing this can net you a lot of money if you know where to look for these trade items out in the wild.
Another good way to make money is to first level up to around level 13 and go back to low level areas and quick-finish battles with monsters that are lower than your current level. Doing a quick finish will finish a battle instantly, thus making it a good way to farm a ton of items from monsters to sell for zenny.
That being said, we highly recommend using this method if you don't mind farming. But if you don't want to farm low-level monsters, the best method would be to farm and sell various trade items in the game.
Check out some of our other Monster Hunter Story 2 guides!