DON'T change at the airport. Their rates are some of the lowest. I suggest exchanging at a cambio or FX trader. Ask your driver if he will stop on the way to Negril for you. Or wait a day then go out yourself - it's easy, give it a try.
In a pinch, some places accept Canadian but give change in Jamaican. The rates vary from day to day. I've had from 85:1 to 92:1.