There are two Chinese supermarkets downtown. In the front part of the store in both is a small desk up on a stand overlooking the store. You hand the money you want to exchange to the person in the booth. I usually ask them what their rate is before I hand them the money to exchange. Their rate is always very close to the bank and generally better than the cambio on the beach rd. I would not exchange more than a couple of hundred at a time. You will find the store and cambios are often crowded and many people are in them or just outside. Always be aware of your surroundings and exchanging $2,000 would draw a lot of attention if they even would do that much. You could also exchange at a bank but the wait times can be long. Cambios and banks will require your passport while the Chinese supermarket will not. The wait is almost always shorter at the Chinese Supermarket. In and out. Your other option is to just use ATM's, while they'll have a service charge you will get the going exchange rate. NCB is one of the banks in Negril. It's in the newer strip mall plaza on the main beach road. It is the most convenient for tourists and has multiple atms as well. There is also a Scotia Bank downtown.