The most common response is, “I don’t have enough money.” This is almost immediately followed by the question, “How much did your trip cost?”
The simple answer is that cruising costs what you allow it to cost, just the same as living on land. Certainly living at anchor is less expensive than existing on the solid stuff a few hundred yards away, but it isn’t free. In six-and-a-half years of sailing around the world, we had one month when we spent almost nothing, and we know of some cruisers who had two or three such months, none consecutive.
There are certainly cruisers who claim to have lived on $500 per month, and good luck to them. We didn’t live that way on land, so saw no reason to do so on a boat, particularly as divorce would have been an almost inevitable result. Anyhow, most such stories are based on selective memories, or faulty math, or both.
We did a lot of land cruising which meant hire cars and hotels. That is the point of cruising, to fully experience the country you are visiting. The cruiser who stays on board in port certainly saves money, but sees only other cruisers.
We spent (for 3 people) around $40,000 per year including every expense.