I used the Aetheryte ring method until I couldn't squeeze anything more out of it. It's basically free and any FC2 you get are pure profit. If your GSM and MIN are leveled, then you should have no problem gathering your own ore/clusters and making your own nuggets.

Once I was capped for rings, I moved to Gold Specs, which where a bit expensive at the time (though less so than Carbuncle Clocks), also make sure to meld them (triple or quad meld if you can) with crappy tier 1 materia to improve the success rate. I rode that train straight to 100.