Upgrade to a bonebreaker and change it to a staff of life, mithril dagger or light crossbow; sell that. Use the money to buy crystals to purchase a luxury store blunt (the more expensive kind), and upgrade that to a yaksa mace.
The two transfers cost around 2.8 mil AA together if I'm not mistaken, but you'd be wasting your money if you took the item from top D to bottom C via Mammon.
Get the top weapon from luxury shop and upgrade that to top C for about 2 mil AA (not sure on exact number). When you have top C exchange at mammon for yaksa. On the other hand see if you can find a bargain top C and trade that instead.