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Try and find an active linkshell that calls out hunts. 4.0s hunts have a chance of dropping a cracked cluster, which can be traded in for level VI materia. Thats a great way to earn gil as high end materia usually sells for a decent amount.
Challenge log:Don't bother trying to do everything on it. Pick out a few of the easier things to do each week as you can get a bit of gil that way too.

Farming mats/skins: Aldgoat/Gigantoad/Boar hides FF14 Gil all sell fairly well usually from 500-5k each depending on server. As a max level character you can get a stack of aldgoat in roughly 20 minutes.

Fisher is an easy way to make tons of money. You just levels this one class to 70, which isn't even that hard or expensive, and then take some level 70 gear even without materia melds and start spearfishing...dusklight aethersands go for 20k at the server, and they sell pretty good. Somebody can fish Final Fantasy 14 Gil like 100 within one to two hours, that's 2M gil. Ivory Sole for the Sushi everyone wants, Swordtip for the crafter buffood... that fisher can't make money is a myth.

Other ways of making a moderate amount of money involve getting lucky with Wonderous Tales. Sometimes Khloe will get you crystals which you can exchange for level 6 crafting materia that will sell for a lot of money. You know why they sell for a lot of money? Because crafting is pretty much the only way to make it!