Okay, I'm in Annapolis, so I'd double Scotty's numbers, but the point's the same. A brand new, 40-something footer from Hunter/Catalina/Beneteau may cost as much as a small house - for comparison. An older boat makes sense; you don't need the latest electronics, etc if you're not planning to do a lot of sailing right away. My personal opinion would be to aim a bit larger than Scotty suggests, in the low 30-feet, much smaller and you're sleeping in the main cabin and cooking on a coleman stove (which feels to me like camping out)
A lot of folks do exactly what you're describing and love it. On the flip side, realize that if you do a vacation house, you can use it 12 months of the year. Count on only 9 months comfortably on a boat; winters are doable but not so much fun.