Cubic zirconia is basically worthless, so it depends mainly on whether the gold value is worth the money. Now the price of gold is about 22 1/g, and yours is 18k, which means the purity is 75%, so your ring is worth as long as it weighs about 2000/221/0.75 =12g. Including some processing fees, I think the weight of the ring is not less than11g.