If you can get into a r45 spiritbond party at one of the strongholds, then you can complete a few sets of armor in about an hour or two. Best thing i can suggest is investing in electrum rings to convert into materia. Maybe you are not made of gil but they should come cheap enough. If you get any Materia IV, they can sell for quite a lot, depending on what stats they increase. Also, if you are a goldsmith yourself, the rings will sell like crazy. Its the cheapest way to make IV materia. Just gotta be able to find the best way to get the most xp.