if you have excess grand company seals you can buy survivor manuals that will boost your xp a lot, you can use them while farming the popular mats so you can make some good xp and cash at same time.

since gathering can be boring you have to spice it up some. buy npc gear and spiritbond it, gather materia is in high demand across all servers. most cant be bothered bonding low level gear for tier 2 materia so you can make some quick gil (which will easily pay for the npc gear) and rebond another set. keep doing this until you get to 60 so you have more than 1 reason to level (exp).

at this point you are swimming in materia, now you can max meld yourself for free.