Alienagw- Unfortunately, your question is a lot like asking 'how much does a car cost?' The answer is 'it depends.' (Are you thinking BMW, or Chevy?) The short answer: If you're buying a new boat just to live on while you work a day job in the corporate world, you probably won't be saving money, between the cost of dockage and boat payments it'll be a wash. But if you love sailing and own a boat anyway, it's a whole different game -- and a LOT more fun.
I can't answer in general, but I can give you some ideas based on the Washington DC area: 2 BR apt rents for about $1100 - $1600/month, electricity $80-$100. Dockage for a 35-40' boat (i.e., 2 cabins): $6000 - $8000/yr in Annapolis or Washington DC; $2500 - $4000/yr in Baltimore or south of Annap. (Cost of said boat, $25,000 - $250,000 and up, so again it really depends on your boat status going into this.) Liveaboard fees (generally include electricity & water & mail) $80-$100/month. Renter's insurance, $300/yr; boat insurance (depends on your boat's agreed value, your experience level, and your cruising area, about $500 - $1000/yr or more for Chesapeake). Cellphone or landline, same costs as on land. Pumping holding tanks, $0 - $5/pump (every week or 2) in season. In winter, use marina's bathouse, or bag-and-bucket, or have someone come to you while your boat's iced in for the outrageous price of $35/per, according to our neighbors. Boat maintenance, figure 5-10% of value depending on complexity of systems, how much you cruise, and how handy you are. You'll probably use a U-Stor-It for all the stuff that doesn't quite fit on the boat, $35-$100/month depending on how much 'stuff' you store. Hope this helps - E.