Looking broadly at the costs to use brine instead of fresh water you'd need a combo of stored brine and a method to generate brine from freshwater (for withdrawals) and then desalinate the brine (for deposits). And that would require quite a bit of infrastructure to store and process the salt generated and used by the freshwater <-> brine process in both directions. Depending on how quickly you want to be able to draw down the SPR you'd need to store a significant amount of salt at the location.

At a maximum to be able to withdraw the entire reserve you'd need 1.3561 × 10^7 cubic meters of halite (this number uses the density of halite as a solid crystal not the density of a pile of ground up halite they'd actually use) weighing 2.94273 × 10^10 kg or 29.4273 Tg (teragrams, a rare treat to get to break out that unit). [0] That number gets smaller when you allow for receiving shipments of salt during the drawdown since they can't instantly pull out the full reserve so they have time to allow for receiving salt shipments.

[0] https://www.wolframalpha.com/input?i=%28714+million+barrels+...