Dock fees generally range between $400-$800 a month, and that usually includes water and electricity. I think sewage is extra.
Best way to think about marinas is mobile home parks plus. Most folks there are just normals tryna get by on the cheap. Very occasionally you’ll get some landlord or HOA Karen type that thinks their shit doesn’t stink, but it always does.
Maintainence is the real killer for the wallet on a boat though. Mobile home units can’t sink, so maintaining the home isn’t as optional as it would be otherwise. You still get sea gypsies occasionally in floating wrecks anchored just off the docks, but that’s everywhere really.