International data usage (background apps refreshing)

I thought I had turned my iPad on airplane mode while on the flight from Miami to the Cayman Islands. I only discovered it was not on airplane mode and was connected to the local cell service (digicel) when I was packing up my bags to head home. It was locked in a safe the whole trip and never used but I had not disabled the background app refresh, meaning my apps were likely still refreshing in the background using cell data without my knowledge. We were here for 4 full days. Att says its roaming data charge without any plan is $2.05/mb, but that doesn't mean much to me. I'm not sure how that translates because I'm not sure how much data is used by apps refreshing in the background. How much can I expect to be charged for roaming charges? Is there any chance I can try to dispute roaming charges since I was not aware this was happening?