So I just train a character from 0 to 300 in jewelcrafting, and it probably costed about 500g in materials, not counting the hours of mining metals I somehow haven't managed to stockpile enough of over the years I've been playing the game.

In short: Leveling JC is freaking expensive. Carefully consider the cost and reward first.

Unfortunately for me, I just wanted convenient access to a gem cutter. I think I could have bought all the gems I'd ever need cut instead...