When buying new it was always $8K where it comprised of $5K for EAP, and $3K for FSD.
Then they decided to have a basic AP as part of the vehicle, and then they made FSD (which incorporated the features that used to be in EAP) $5K. Then that went to $6K without anything to show for it.
For existing owners the upgrade charge has always been all over the place.
As to the take rate that's a good question.
It used to be REALLY low like well below 30%.
But, the take rate for EAP was pretty high. Then when they changed things up they made it fairly cheap to upgrade from EAP to FSD. I think it was even briefly discounted to $2K if I'm remembering right.
So that may have pushed FSD to 30% that you estimate.