There is a vast range. The Pardey's still cruise on about $1,000 per month. Larry tells me there are young people out there doing it on $600. Annie Hill did it for years for about $3,000-$4,000 per year, but that was a pretty austere lifestyle.
Eliminate as many gadgets as you can (they all will break anyway), and at every possible turn simplify. Don't shop. Stay out of chandelries. Look for low cost alternatives. Do it yourself. Eat beans. Read everything written by the Pardey's and Annie Hill. Stock up in cheap countries.
The "solutions" sold and advertised for "safer" or "easier" cruising - fancy electronics, watermakers, digital this and that - all will consume huge amounts of cash. It is all a load of marketing BS. VHS radio, GPS and EPIRB are all you need.
My biggest costs and headaches have been engines, refrigeration and sanitation systems. I got rid of the fridge and put in a composting toilet. Much better. In the Carribean you could even go without an engine, if you have the skills.
Cheap cruising can still be done. With boats at rock bottom prices the time is now, if you can swing it.