I've never seen a pay ramp, at least not yet.
Here in AZ, bodies of water seem to fall into 4-5 different categories:
State - Your AZ boat registration gets you on these legally.
City/County - depending on the specifics of the water, your state reg may get you on, if not, you may need another decal. (i.e. There's a city-run lake-development thing here north of me, crap for fishing, but it's only a 10-min jaunt to get the boat on the 2-3 miles of water. Not too bad for taking newbies and kids out on the boat. I MUST have an AZ reg to get their decal, which is $5/year to residents, a lot more if you're not.
Native American (or whatever's PC now) - to legally put your boat on their water, you must have a "watercraft permit" from the tribe, to the tune of $5-8/day (doesn't include your tribal fishing permit). They don't care if your boat has a state reg or not. My buddy was pretty sure his inflatable raft didn't need to have a permit on the res, but I looked up their "Game & Fish" equivalent, and the law pretty much says that if it's on the water it's watercraft, thus needs a permit or will be confiscated.
Private - Sure, some people own land with their own bodies of water, and we have a lot of man-made lake communities, but without residence, or an invitation, you can't use these waters. We don't have any pay-for-use types of lakes around here that ya'll speak about.
Other - Not sure if it's state or federally controlled, think federally, but as we have the Grand Canyon here in AZ, I know that there exist some oddball boating regulations on the Colorado River. I believe that you have to have a special permit to run the river. Not sure what it costs, or what the craft limitations are, but I wouldn't want to take my tin out on rapids for nuthin' :shock:.
Anyway, thought I'd share.... 8)