Why not make a solar-electric narcosub? That way you don't need fuel, and you're not relying on an IC engine with a bunch of moving parts, and that has a heat signature. The sun is shining in the ocean that these cartels are sailing in anyway, so there should be power.

Steer with GPS, that way you are only listening.

I wouldn't rely on Starlink, it seems like something that could be discovered easily. Any authority that had a map of where legit ships are could filter down to the mysterious Starlinks that are in the middle of the water, but near a remote coast, having traveled from Colombia, not on a known vessel.

Maybe if you need the comms, you rely on radio. Whatever the ham radio people use could perhaps be made into something. You don't need a lot of bandwidth anyway.

I guess the question is economics, then. How many trips could you get on a little boat that has a solar panel, electric engine, a battery, GPS, and a radio? And what would that cost?