The only gil-sink is Repairing. Provided you level your Crafting and Gathering professions, you can repair for free. So, it's really just a race of trying to sustain yourself with the Gil you make from normal stuff until you can do it all yourself for free. Some people think it's reasonable for everyone to have a million gil and be level 50 and raiding Titan HM a week into projected launch, which is stupid. The economy is sustainable potentially because every character has it within their power to be 100% self-sufficient economically.