If you were to go old school like I prefer to do (I even still write checks in some cases & pay cash whenever possible) and call them direct you would find that they - the manufacturer of this TPMS - are absolutely not out of stock as well as you just might be happily surprised at the final shipped-to-your-door price with a little human interaction.
And if that still isn't your cup of tea Amazon beats both of the places you posted above.
Not much more I can add so do with the info. what you will my friend.
And believe me when I say that the verdict will be out on this TPMS for a very long time for me. No endorsement or final review here. Just one long ongoing review.
I just hope that it's there for us when we need it most - like before, during, & after a blowout - unlike our previous TST TPMS.