Refugee market
There are people in Cuba, Haiti, and other places that would like to leave. Some of these are paying like $10,000 each to get smuggled into the USA. Seems the money usually comes from relatives inside the USA.
If seasteads could get as cheap as $40,000, then some families might buy one instead of paying to be smuggled into the USA. A small seastead like the Ball House might get that cheap.