Well, if you can find an ATF that says it meets Mazda FZ ATF specs, I'd really appreciate it if you'd post the info here.
As to the person who wrote that about the Skyactiv tranny reman facility, what they failed to post probably goes something like this: Most of the Skyactive A/Ts that need rebuilt have pure Mazda FZ fluid in them.
That neither means that the non-Mazda fluid caused any particular failures, nor that the FZ fluid is not good enough. It simply means that a percentage of transmissions fail before they should. There isn't enough info to draw any further conclusions.
I sympathize with your situation. The price you posted for the Mazda fluid is insanely high. I don't know quite exactly what I'd do if I were in your situation, but there have been some good suggestions here (i.e. see what the dealer will charge to change the fluid, making sure they will use Mazda FZ fluid).