As for $16-$18 to launch your boat being a total ripoff, go check out the cost of storing your boat at a marina. $18 seems pretty reasonable to me.
As for those that want hourly fees, be an entrepreneur, find some land near the entrance, buy it, build a parking lot with parking meters, staff it so as to write tickets to those that stay past their alotted meter time and see how much you have to set the parking fees to make a profit.
That is relatively cheap and besides if you plan to use a boat you will likely use it more than a half dozen times which is where a annual pass works.
For comparison, in\out ramp fees at Tahoe Keys Marina in South Lake Tahoe are $35, Cave Rock, NV on South Shore is $12 but all ramps require a mussel inspection that ranges from $10-60 with most boats costing $30. Folsom and the Sac river are cheap especially with a pass.