Instructions
Defeat enemies to receive easy gil. Once you reach level 20, enter the world map and you can set up your controller with a turbo function. Press down on the down, left, and x buttons. This will cause your playable character team to continually walk around in a circle, encounter enemies, and attack them. At this level, in a weak enemy zone, the team will not incur much damage, so you can set this up while reading a chapter of a book or cooking lunch.
Complete the Chocobo Hot &Cold Side Quest. At Chocobo's Paradise, you have the option to talk to the Gold Chocobo. Obtain the Dead Peppers and sell them at item stores. This can be done endlessly for easy gil.
Play the Chocobo Hot &Cold games. Upon winning, you will receive items. Sell these items for gil.
Enter Lindblum's theatre district. Turn and enter the gang hideout. Three chests contain gil for the taking. The sum of these chests is between one and four thousand. The chests also restock occasionally.
Visit Dali and purchase 99 Wrists for 130 each. Go to Lindblum and purchase 99 Steepled Hats for 260 gil a piece. Synthesize these items to make the Cotton Robe, which costs an additional thousand but sells for two thousand gil. The net profit on each robe is 610 gil, meaning 99 Cotton Robes will net you 60,000 gil.