According to SpaceX, the cost of putting a pound of things in space is around $2,000 to $3,000. The astronauts are only allowed to take only 3.3 lbs of personal belongings to space, all of which comes back with them.
Astronauts are not allowed to take any foul-smelling thing with them. and there is a man at NASA whose job is to smell everything that goes to the space station. In the closed system of ISS, the air has to be re-circulated. Anything that smells bad can make the lives of the inhabitants miserable. Therefore, only those things are permissible that pass the smell test by the chief sniffer, George Aldrich.
We can’t identify all of the things that would ultimately, smell bad, but NASA’s ‘smell man’ knows them. CDs are made with plastics that produce unpleasant odors that we can not identify in ordinary conditions. Even some clothes, shoes and food items get rejected for this reason. A book or paper item that has absorbed unpleasant smells is forbidden. As leather is in fact, treated animal skin, so, it gets rejected too. The personal grooming products, inks from pens and markers go through inspection as well.
You will be happily surprised that after all the strict checking and everything, what these astronauts have already taken to space. Ranging from a six book library to guitar, electric piano, Lego, fruitcake and even a box of Christmas decorations.