"Compared to lithium-ion batteries, sodium-ion batteries have somewhat lower cost, better safety characteristics (for the aqueous versions), and similar power delivery characteristics, but also a lower energy density (especially the aqueous versions)."
https://en.wikipedia.org/wiki/Sodium-ion_battery#cite_note-:...
Also, recent CATL PR releases about sodium ion only mention 'future cost savings' rather than anything about a 90% reduction in prices.
Hyperloop was more of an after-the-fact reaction to California's high speed rail project, which started 17yrs ago (2008). Five years before the Hyperloop white paper was published. Hyperloop came out 2013, not long after the 2012 announcement that the rail project's cost would double from $8B to $16B and it was already facing delays. Elon explicitly said he didn't like the project and it inspired him to look into alternatives.
Also, recent CATL PR releases about sodium ion only mention 'future cost savings' rather than anything about a 90% reduction in prices.