Frankly, Carolyn and I can't comfortably cruise on $100 a week anymore. We used to, happily, in the 1970s. Now, $1,000 a month is a more realistic bottom-line figure for maintaining our personal cruising comfort levels.
The less money you have, the harder you have to work at it. We don't have a watermaker, so we endlessly lug jugs all around the world. But this allows us to meet people. Ditto for riding the bus, walking long distances, and bargaining in the local markets. And being fortunate enough to lack refrigeration allows us to save wear-and-tear on the engine, batteries, and electrical system, not to mention the savings in diesel fuel.