With the current situation of huge zergs chasing FATEs around most zones, the easiest way to make money is simply chase FATEs around in a FATE party for a few hours. You'll get a lot of XP that way too, you'll get Grand Company seals you can exchange for gear without spending gil, and you'll get some moderate amount of gil. A person can probably pile up 1,000 gil from FATEs in an hour or so of chasing them around with the zerg.