A raft can be really cheap to own, too. While it is possible to have a big boat and not spend much money, I think that particular big boat would not be one I'd want anything to do with as it will either be so minimal I wouldn't want to use it or, more likely, in really bad condition.
Expenses like moorage, insurance, power (in some harbors), and haulouts are all going to cost more as boat size goes up. Sure, you can put the boat on a buoy--- maybe--- but most boaters aren't going to want to screw with that. And regardless of where it's sitting, the insurance and haulout fees will be the same unless one has cockamamie ideas about careening the boat on the beach to repaint the bottom.
Most recreational boaters aren't going to want to camp out on a boat with a Coleman stove, a jug of fresh water, a sleeping bag, and a bucket to poop in. So while they may not have or need satcom or watermakers, they want a galley, heat or AC, a fresh water system, head(s), a shower, lights, most likely entertainment like music and/or TV, navigation and communication equipment, and so on. And all this stuff requires maintenance and occasionally repair. And the bigger the boat the longer and perhaps more complex the wire runs and plumbing runs and the more sinks and toilets and lights and so on there will be.
Which is why when we decided to get a cruising boat we followed the advice I read in the 1960s in a boating story in Boy's Life magazine which was "buy the smallest boat you can afford." Which does not mean to buy a boat that's too small for your requirements, but that the smaller a boat you buy for x-dollars, the newer or in better condition it will be.