Is jewelry really cheaper in jamaica vs USA? Good Shopping around runaway bay?

I booked my trip to jamaica last week. i will be going to runaway bay in december. I was told from people who have went there that jewelry is cheaper there vs in the USA. My concerns are 1. is it real? I was told diamonds as well as nice watches citizen, tag huer, etc. I would like to buy my wife a nice piece of jewelry maybe spend around $500 just wondering what i could expect to get? I would not be shopping at the resort. Also say the person has something priced at $750 how low can i expect to get with haggeling? Any good shopping areas around runaway bay? Im staying at the grand bahia principe.