Tour Guide - Santo Domingo
I met a guy last Summer who rented a car and paid a local guy to drive him around, show him the sights, "watch his back" basically and make sure that he went to all the right places and none of the wrong ones. Once the local guy dropped him off for the evening, he took the car and came back to meet the guy at breakfast. If the guy wanted to go to Boca Chica, he was driven there, told the local when to pick him up and Mr. local was off to do his own thing for half a day.
The local was paid $200US for the week and the guy who used his services couldn't have been happier.
There are many, many tourists who are not self sufficient and would be willing to pay this kind of money, even more if the guide provided a late model vehicle and cut the tourists costs even further. If you're going to spend a couple Grand on a vacation in a dangerous but fun place by yourself it would make sense to many to spend 15% - 20% of it on this level of convenience. A guy with a decent auto, a legal firearm and a good grasp of the language, customs and lay of the land could turn a third of what the OP is talking about investing into a profitable entrepreneurial endeavor.