You can go to the lost city of Zanaris, in there there is a Gem shop. You can bring tons of nats, and 30k cash. You buy Ruby Rings from the store, then alch them. I did this when nats were 235 or so each, they've gone down lots since then. At the time, depending on how much I paid for nats, I lost 15-30 Gp. With the current price of nats, you will lose 0-15 Gp depending on the price you pay for nats.