Re: $3000/mo cruising budget
A lot depends on where you want to be. If you're not on Medicare, good medical insurance can still cost you $1000/month. Depending on your health and any pre-existing conditions, there's room for a lot of variation in that. And if you're outside the US, the whole picture changes again. Changes from year to year, too, as some countries are now requiring that you have your own insurance rather than burden them.
Then there's where you stay at night. Let's say a 35-foot boat, and marinas easily ranging $2-5 per foot per night for transients. $70-175 per night? Split the difference and say $125 per night, and five or ten or is it fifteen? nights at a marina can rip your budget up.
I think the bigger question is not whether anyone can cruise on any particular budget, but whether you can cruise in the style you want, in the places you want to go, at whatever may be a realistic budget for that.