Gateway Spaceport is a membership funded organization that wants to create next-generation space stations.
Nextbigfuture has written about their earlier designs for an orbiting spaceport.
They have made nice renderings and animations of their designs and construction methods.
The Gateway Foundation newest design is similar to an Icarus Interstellar proposal for a 10,000 person worldship. The proposed worldship had 40 modules that were 120 meters by 155 meters.
A few years ago, Nextbigfuture had indicated that a simplified and more near-term version of the Icarus proposal would be to use expandable Bigelow modules on a basic frame. The newest design from the Gateway Foundation follows the simplified approach of creating a metal frame and attaching Bigelow modules.
The Space Station has 24 Bigelow space station modules.
The space station could use BA 330 modules or BA 2100 modules. It would take 50 launches for two BA 330 modules at a time and launches for the frames and other components. It would take 100 launches for BA 2100 modules.
A SpaceX Super Heavy Starship could launch one Bigelow 2100 space module. The pressurized volume of single BA 2100 module is 2,250 cubic meters (79,000 cu ft) which is more than two times larger than the 931 cubic meters (32,900 cu ft) volume of the whole International Space Station as of May 2016.
Each module could hold 10 to 30 people for extended stays. The rotating space station would hold 240 to 800 people.
The total cost of the space station could be in the range of $5 to 20 billion if each of the SpaceX Super Heavy Starship launch costs were in the range of $7 to 40 million.
Costs could be lowered by only using a frame and two opposing Bigelow modules. This would allow the space station to be scaled as partners are found for each module. The initial frame and pairs of modules might be reduced to three launches.
One launch might be able to handle a simple and lightweight frame and teleoperated robots. The next launch would include airlocks and other parts of walkways. A final launch would include two Bigelow BA 330 modules.
A basic rotating space station cost could be in the $500 million to $1 billion range.