When we head out in August for a few years, it will be in a two-year-old boat that is fully paid for, fully fitted-out and with three years remaining on its warranty. Because of the newness and the warranty, repair and maintenance costs will be low initially, and I'm estimating $5,000/yr until the end of the warranty period.
Careful there. That warranty is 5 years against hull blistering. Most everything that actually might go wrong with your boat will have a one year warranty (engine, genset, electrical system, plumbing, steering, etc.). I'm not suggesting that a newer boat won't have less maintenance costs, but it won't be zero, particularly if you are cruising full time.
I also think some of your numbers might be low, but I don't know for certain. It all depends on what you want to do. True, if you are going to sail harbor to harbor, drop a hook, and spend money on nothing but food and drink that you cook yourself (the food part that is), you probably are right. BUT, if you want to explore inland at all, if you want to eat out every now and again, if you want to socialize in town, if, if, if, then you likely are going to have greater expenses. Again, this is my opinion; I do not proclaim to be an expert in this (though I hope to be soon enough!).
I actually thought Architeuthis' post was pretty good, and I took him seriously. You can argue around the margins for sure, but I think the thrust of his point is that if you are the type of person who goes out to eat twice a week, goes to two movies per week, and stuff like that, it's not particularly realistic to think that you will stop doing everything you like to do just because you now live on a boat. No doubt, many things will change and you will enjoy many things that now will be free (sunsets, swimming, fishing, gamming on the beach), but I think it might be a bit romanticizing to think you will go from the quintessential suburban consumer to a minimalist.
I do hear the criticisim that if you don't maintain a shoreside home cruising should be at least somewhat less expensive. I bet that's probably true for the time you are out, but what about when you come back? I think that's his point too. Getting yourself back into the mainstream, on whatever level you plan to come back, costs money too. If you sell your house to go cruising, cruise for 10 years (just to pick a number), and then come "home," you will need to buy/rent a place to live, and that equity you had in your house will be gone. So getting back ashore is a cost to consider.
I think it certainly is possible to cruise less expensively than it costs to live ashore, but I suspect that in the end, for most people who actually go, that's not the case. Soup to nuts, all in, take two families from the same socio-economic bracket. One steps out of the mainstream in the middle somewhere and takes a 5 or even 10 year cruise, and the other just works and lives "traditionally" straight through till the end. I bet the total amount of money they spend before they die probably does not vary all that much (and the one that did not go cruising probably has more money in the bank at the end, even though the happiness tank might not be nearly as full).
Just my uninformed thoughts on the subject.