31, yellow gold
Was going to go with white gold, but the jeweler clued me in that "white gold" is usually just yellow gold with a nickel or rhodium plating. Not wanting to pay more for a ring with plating that might wear off eventually, I just went with the traditional. And you know what? I kind of like it better having a classic looking ring.
You do you OP, go for a cheaper metal if it suits you. At the end of the day, no one gives a shit what your ring is made out of. It not part of your overall "look", it's just a quick signal to others that you're not available.