The pricing matrix for iPhone will be more complicated and expensive, such as:
32 4" @ $599
64 4" @ $699
32 4.7" @ $749
64 4.7" @ $849
32 5.5" @ $899
64 5.5" @ $999
128 5.5" @ $1199
And I am being conservative here.
No, I don't think you are. There will definitely be 16 gb options available, if only on the legacy (5c / 5s) models. I'd expect that to start at $450 off contract, just like the 4s does now.
No reason to think the base model 6 will cost more than every base model apple has ever released since iPhone 3G: $649. Whether that base is 16 gb or 32 remains to be seen. Let's play worst case scenario: it's 16 gb in the base 6, and apple keeps the $100/storage upgrade, and they have the $100 premium for the 5.5", and there's a 128 gb available. That makes the 32 gb 4.7 $749, the 32 gb 5.5 $849, and the 128 gb 5.5 $1149.
And that's a lot of negative assumptions (premium for the 5.5", maintaining the $100 storage bump costs, and 16 gb base model).