The existence of the Model 3 is predicated on significantly lower battery costs, plus an increase of 30% in battery size will add less additional kWh since base battery size of Model 3 will be smaller than for Model S. Between these two effects, I think we can expect a battery upgrade in the Model 3 to cost roughly half of what it has been for the S.
Maybe a lineup something like this?:
$35,000 Model 3 60 (~280hp, 230mi)
$39,000 Model 3 60D (~300hp, 245mi)
$41,000 Model 3 70 (~280hp, 270mi)
$45,000 Model 3 70D (~350hp, 275mi)
$50,000 Model 3 P70D (~450hp, 275mi)
$60,000 Model 3 P70DL (~550hp, 270mi)
I wouldn't be surprised for the base model S pack to be upgraded to 85KWh, and the premium pack to go to 100KWh. An 85KWh pack produced at the gigafactory will probably cost less than the 70KWh does today.