The "over $500" applies only to RESIDENTS (JA passport). If you're a visitor, you are specifically asked whether you have gifts or articles for sale, regardless of value - the determination is to made by the customs official.

The form is at http://www.jacustoms.gov.jm/docs/n_C5Update.pdf

Duty rates are not available online. Do bring your receipt, in case you can get them to accept what you actually paid as the value, rather than what their chart has as a value.