Does anybody have an idea about how much it would cost to build an artificial island or floating island (seastead) per kilometer square or per mile square? How many millions does it take to start your own country, just for the physical infrastructure?
That depends on the design, you might design something in steel which would be expensive as well as requiring constant maintenance or you might design something that is cheaper yet will have a limited lifespan and need to be replaced after so many years.
Do you really want such a large single structure, maybe it would be better to link up 2500 rafts each 20mtr square to create your 1Km square island.
Your island could start small and grow as funds become available or demands dictate.
The Monaco Breakwater cost roughly $1580 per square foot, or about $1.5 million per 1000 square feet. It was floated to location. However, it has a lot of “extras”. For one, it is a breakwater and not a permanent floating structure. It contains a shopping mall and parking garage. The Surface area is 90 feet by 1000 feet, so it is an area of 2 city blocks.
For my story I needed to do a cost analysis. I can’t find it right now, but as I recall it was about $1 million for every 1000 square feet. There are 10.7 million square feet in a square kilometer, so about $11 billion for a square kilometer float.
Seasteading institute has a whitepaper showing cost models. I figure a basic floating apartment with 32 units would need to cost $1 million per unit for the float. The building on top is relatively inexpensive in comparison, just $200k per unit or so.