The plan for the ISS upon decomissioning is to deorbit the structure and let it fall into the ocean.
I get that we do not want extra debris in orbit but I would think that leaving the structure in a stable orbit may provide an opportunity to recycle/reuse the infrastructure in future missions. It is expensive to get things of this size to orbit, but if it already exists then it makes more sense to me to leverage the existing assets where possible.
So what would it cost to keep the ISS in orbit? I am not looking for total operating costs, or what it would cost to keep it operational, just the amount that it costs to maintain orbit. What would it cost to put it into an orbit that would be highly unlikely to create a problem for 100+ years? Would that even be possible?