Microsoft has come out and said that the cost of 1TB of expandable storage for the Xbox Series X|S will run you a lofty $219.99 (USD). This expandable storage will come in the form of small cards that will slot into the rear of both the Xbox Series X and the Xbox Series S. They will match the internal SSD speeds and provide 1TB of additional storage capacity.
If you're wondering why the storage is so expensive, knowing that it is proprietary...