I'd point out that P101 and P103 also have "BTR" in their part numbers, while P105 and P107 do not.
I'd, therefore, speculate thusly:
Thoughts?
....- P101 and P103, would be Wi-Fi and Wi-Fi + Cellular, with Retina Displays, making them "Better" than P105 and P107.
As for pricing, I'd speculate starting at $249.
+ $50 for more storage.
+ $100 for Cellular.
+ $100 for Retina.
+$100 for Retina is unlikely. Pragmatically "Retina" means pixel doubling in the context of Apple. Pushing the 7.8" screen to the same number of pixels as the iPad 2012 would mean driving into the 400+ ppi zone. I don't believe that is going to happen for under $100 with Apple's margins built in. In fact, not sure if there are any over 7" screens with that resolution at all even in demonstrations.
Just taking the number of vertical and horizontal pixels from the 9" iPad 2 down to 7.8" is going to increase the ppi. In that "Retina" sense, just shrinking the screen is already "Retina". I'm not sure the point of "Super Duper Retina" at 400 ppi.
The LTE frequency space is fragmented. Apple can't really get around that since they don't own it or provide it. "BTR" , better, could count just as easily mean frequency coverage ( from a specific perspective).