there is no static cost to store oil, there are way too many variables.
If you didn't already have a contract for space and tried to buy space now, you would have to pay the largest amount that has ever been charged to get a contract. The people who own the space are well versed in the spreads and will capture the lions share of the spread.
The guys making coin on space right now are the ones that hold long term contracts and have had them for some time. (before the market went deep contango).
For future reference, there are no standard costs in anything related to energy, from royalties to drilling costs, everything is negotiated and never stays static.