Finance and Business How much does a 1.5 carat diamond cost? How much does a 1.5 carat diamond cost? To sum it up, a 1.5 carat diamond can range anywhere between $5,000 (a cheeky Cushion) and $35,000 (a Brilliant Round). And the best value option should cost anywhere between $8,000 and $12,000. Related Posts:What size is 1.3 carat diamond?How much does a 6 carat cost?What is a 1/5 carat diamond worth?What does 1/4 of a carat mean?