I spent a couple months living on a sailboat off the coast of Colombia and Panama last winter. I was crewing for somebody, but it was easy to see that it wouldn't take a lot of investment to get up and running on your own.

Worth knowing, from a developer perspective, is that Colombia has really good 3G coverage. Unlimited mobile internet access will run you on the order of $20/month, and it's available pretty much everywhere. Including anywhere you're likely to set up shop on your boat.

The San Blas off the coast of Panama are where you really want to be, but unfortunately the internet access isn't so great. You can get online in a lot of unlikely places (there are islands with literally nothing except coconut trees and a solar-powered cell mast), but it will cost you.

Head to Cartagena and ask around at Club Nautico. Chances are you'll find somebody who knows somebody who has a boat to sell.