Welcome aboard Snkr.
About a year ago I was asking the same questions, or at least researching the same subject.
From what I've gleaned, $500 per month is doable and members here like Zeehag and Boatman have developed it to an art form. They do it with some talent and flair too, and with dignity and some rather warped humour...
Most would not have the skill or temperament to get out there and do it like that.
Many more are doing it on $1,000/month, and the ones with budgets of $2,000/month are considered to be doing it in some style with trips home occassionally and the ability to do more touristy stuff as they go.
It will make a significant difference if you are cruising the east or west Caribbean
, east or west Med. or Pacific islands etc.
All the above assumes you have a sound boat and tackle most maintenance