I once read a case study about a consultant that would go through the warehouse/part storage facilities for the businesses that hired him with the top management in tow. He would ask how long a particular item had sat in storage and when told the time he would measure the footprint and then write a dollar figure on a label that he would stick to the item. He knew the cost per square foot per year and could calculate the storage cost pretty closely. When he was done he made the management go through and total up the bill. The end result was a renewed focus on storage costs, making JIT (Just In Time) part deliveries a very attractive option.
Having run a a mini storage facility for a number of years I can tell you for real that it costs money to store things, and you, the customer, pay for it.