Final Fantasy XIV: A Realm Reborn will completely rewrite the in-game economy and Square Enix has kindly broken down exactly how it will do this.
The changes shrink down the size of the economy to move it in line with a brand new launch, they also cut the wealth of current players. The full changes are below:
Upon the release of FFXIV: ARR, we will be removing one zero from all gil prices, in a process known as Currency Redenomination.
1. All NPC vendor buying/selling prices will be reduced to 1/10 of current values.
2. All quest rewards, monster drops, and in-game monetary rewards will be reduced to 1/10 of current values.
3. All repair costs, airship fares, and other in-game service fees will be reduced to 1/10 of current values.
4. Because of changes to game systems, the prices of existing items will change to varying degrees.
5. The maximum amount of gil that a player can possess will not change from 999,999,999.
6. The amount of gil required to obtain certain achievements will be reduced to 1/10 of current values.
7. All gil currently held by players will be reduced to 1/10 of current values.
Example: A player carrying 100,000 gil will only possess 10,000 gil upon release of FFXIV: ARR. However, a chocobo rental fee of 800 gil will be reduced to 80 gil, and an NPC previously selling an item for 1,500 gil will sell the same item for 150 gil. The effective purchasing power of your savings will not change.