Here's my experience from last week. I both traveled with cash and changed it at the cambio, and used the ATMs at ScotiaBank to withdraw JMD 30,000 at a time.
The ATM wins!
ScotiaBank charged me JMD 545. as a transaction fee (roughly $4.50 US).
My credit union charged me $1.50 US as an out-of-network fee.
The exchange rate was the interbank rate as of that day (so around 121.5 JMD per USD).
The cambio next to the bank was discounting the exchange rate by roughly 3% (a bit over 118 JMD per USD).
I was withdrawing $30,000 JMD US at a time, about $250. US. The net effect is that for these transaction amounts, it was about $2. US less to take JMD from the ATM than traveling with cash and changing the cash at the cambio.
Of course, if you do more smaller transactions at the ATM, the fees are going to eat up more of your money. On the other hand, if your bank is "in network" with the ATM you're using so the fees are lower, you will do even better to use the ATM.
Taking US dollars out of the ATM then changing them at the cambio will always be the worst strategy.
Of course, the guys hanging around the cambio were offering an exchange rate of 120...
