Up in the air

Who knew? And what are the requirements? Reading a story today about a woman who had been tricked into paying money to a “cosmonaut” who couldn’t afford to pay for his “return ticket to Earth” from the ISS, it said that space travel didn’t work like that … you don’t have to buy your own ticket. The amazing thing, though, it seems like private astronauts (and cosmonauts?) can pay for their own tickets to board the station. The price does include a return trip to Earth. I knew you could buy tickets to travel to "space" with Space X and other companies, I just had no idea you could buy a ticket to the International Space Station. So how much does it cost? What are the requirements/restrictions? And how much would it cost to take a Fisher Space Pen on board and see if it really does write in space.