Take a look at Hip Camp. It's various folks offering places to stay. Never know what you might find there. Hip Camp gets a cut of the fee to support the page and that's fair.
Here is a guy on that site who is offering a free place to stay with a posted
price of 10 a night.
https://www.hipcamp.com/en-US/land/f...s=1&children=0
In Sebastian you'll find
Captain Hiram's on the water. We used to beach our
dinghy there for some very low weekly rate and use the showers and leave a car in the lot.
Might be better to launch and then ditch the trailer at Cracker Boys Boatyard in Ft Pierce but they weren't
cheap. Someone will likely have a better idea for you.
One big caution from my youth of camping on the beach north of Ft Pierce is be ready for sand flies. They used to drive me to drive about 2 am on a windless night. Worst biter in that area and merciless being 80% jaws. Instant pain!
Good Luck!!