To easily earn money, go to the Lost Village and kill some Axe Armors until you receive an axe. Then, go to Yoko's place and upgrade the axe into the Battle Axe. Next, upgrade the Battle Axe into a Bhuj. It can be sold for 10,000 gold at Hammer's shop.
To easily earn money, get the Mimic Soul and go to the bottom right corner of the Clock Tower. There will be a save room and a spike pit. The Mimic Soul will usually give you 500 gold each time you are hit by the spikes. When you are low on health, go to the save room nearby and heal. Repeat as desired.