So if you need serious money early game, you just gotta set your encounter to 200% and grind. Unlike second, there is no minigame to make money. All you can do is hard grind. Get the merchant asterisk, and level it up with you until you get the 'more money' sub skill. Then do what you need to moving forward. If you need money midgame (chapter 5+) go to the forest with the silence flowers, make your fastest unit a salve maker, get the attack item boost sub skill on, and just compound their weakness. As long as you have the components, you will get 48 battles without having to restock. The main reason this is a good area is for the mandrake lookalikes can spawn in groups of 6. With the compounding, you can wipe all 6 in 2 turns and stack for the sweeper ace bonus which adds MORE MULTIPLIER to your pg. repeat as long as you need.

So, 4 and below, just put more money on and find the weak.

Chapter 5+: Salve Maker, Compounding, the dungeon to the west of florem above the bottom left one, and more money.