Going from UK experience, you'll probably need a permanent berth somewhere, which will be expensive if it's a marina, less so if it's anchorage (but much less convenient). If you're at work full time, this will be a necessity. Most marinas have a different rate for residents than for leisure boaters. You will have to pay visitor's fees at any owned buoys or marinas you visit although in the UK this isn't expensive for one or two nights. You can always drop a hook at anchorage to avoid fees but you have the problem of power. You can have a wind generator to keep your batteries topped up when you're at anchor but in my experience they don't charge the batteries as well as mains (some converters are much better than others). Also if you choose the anchorage option you have to go ashore by dinghy if you need provisions, so paying a bit more for a pontoon is probably worth it when it's pissing with rain or choppy. You have your fuel on top of that of course. I don't know the system in the US but in the UK you can wangle cheap marine diesel if you sweet talk your fuelling marina(s). Boats tend to be a sinkhole when it comes to money for upkeep, so you'll need a contingency fund for when bits inevitably wear out.
On the whole, once you've paid the main outlay which is the cost of the boat, it works out much cheaper than owning a house, provided you don't mind living in a tiny space and everything smelling of damp.