Hamilton Island is U.S. government property. No fees and no permits, and it's maintained by the COE. Exceptionally good parking and an excellent ramp, but it can be tricky during high flows. Access is via Hwy 14.
Somebody mentioned Cascade Locks and doing a lock-through. Forget about that--the Corps will only lock private boats through at specific times twice a day, unless they've changed policy, anyway. Or, if you can piggy-back through with a commercial boat that doesn't take up all the lock space.