Would be a set of Marvelous Pigments. You can create up to 1,000 cubic feet of actual permanent material, and one of the things you specifically can create is Lead. Sweet, Delicious, Inedible Lead.
Considering the initial 4,000 gp investment for the paints, the option to get a freebie Philosopher's Stone every month, with Lead weighing 708 lbs per cubic foot (or so the internets tell me), you could conceivably create 35,400,000 gp worth of gold! (That's 35,396,000 gp of profit.)
Yeah, so it takes you 59 years to convert it all, but we're talking long term investment, aren't we?. 600,000 free gp a year is nothing to scoff at.
Note: This is not a criticism of the class! You're giving up some very appealing alternatives to satisfy your lust for lucre.
I would prefer immortality myself. ~shrugs~ But greed is good too. ~thinks~ Maybe we should convert the Runelord of Greed to an
alchemist.