The slowest and cheapest method is floating, whether on a sailboat, rowboat, motorboat, or experimental rocket-powered hydrofoil. Boats typically have speeds of around 10-30 knots. Thus a seastead just outside the 12 or 24 n.m. territorial water limit could be reached in 0.5 - 2 hours. Getting to a seastead outside the 200 n.m. EEZ would take around 10 hours. More distant seasteads would require days of travel.