You can make your own 45+ crafting gear and go spiritbind it by either spamming lots of HQ items or by killing mobs, then convert it for the materia you need. Profit will vary from server to server (and from time to time) so it's up to you to survey the items you can make and see which are profitable for you. In general, HQ materials tend to net decent amounts of gil (e.g. HQ Wool, HQ Felt, HQ Twinthread) but that requires you to be able to consistently HQ them.