The prices in my post are for Washington and British Columbia area. I suspect that prices vary wildly by region.
I have a 40 foot slip now and pay $212 a month plus electricity. In my old 30 foot slip it was $160. When I lived in Seattle a 30 foot slip at the port owned marina was about $250 and at the newest marina it was about $350, but included cable for what thats worth.
If you meant guest moorage when visiting marinas or parks while cruising about, it varies wildly. At a mooring ball in a state park it costs $7 a night or $11 on a dock up to 36 feet. Marina''s I have stayed at have charged me from $11 to $45 for a night at their docks with electricity. Showers usually are about a dollar.