I feel a case can be made for low cost cruising and budgets but before one can do this they need a means to make it available. You would not have to have vast wealth but enough reserve or an escape path that will enable you to do so.
Less face it if you are in poor position and income it will cost you more to live. This sounds like a wild statement but think it over. You will not be able to hold out for a deal you will have to pay the "interest" and the cost of being poor. Your choice options and time will be limited.
I think this is a very valid point to make. $6,000 a year is poverty. People get trapped in poverty, lose all of their financial resources and sink to subsistence living. If you want to go cruising and can only scrounge up $6,000 a year you need to carefully consider the ramifications before you quit the day job and sail off into the sunset. Clearly, after all has been posted here, there are many variables that will determine what will be your real costs. But, if you want to test the $500 a month theory, you need to have an emergency fund that will get you home and back in the workforce and do not use those funds to fix the boat or buy another month or so in paradise.
Over the last few years I have watched an acquaintance spend down his financial resources while cruising through life. When the handwriting was on the wall, he tried working, but only lasted a few weeks at McDonald's, lost his apartment, moved in with his aging parents, and now his car has failed. This is an intelligent person with a college degree, he just never adjusted to the world as we know it. He might have done better in a low cost area of the world, but I think the end would be the same. He is trapped in poverty and as a fifty-something will always be trapped.
My experience is that it is more expensive to maintain a first world life style in a third world country than in a first world country. Maybe living on a sailboat insulates you from some of those costs, but many are still there.