I think others are giving bad advice. It's easy to get phones unlocked, and then you will have it available not only for this trip, but for other future ones.

Go ahead and get the cheaper roaming option, if you need to use it, but if you can, definitely buy TIGO SIM. And 125 MB is nothing. In two weeks, you will probably use 500 MB, which means 200 USD for the roaming option. But do check TIGO's pre-paid data rates before you decide -- sometimes they are not that much cheaper.