Using more white does not affect battery life on standard LCD displays. It technically takes more energy to make black since the LCD must block out the backlight which is always on. AMOLED does use less energy with black screens.
I think we will see this price structure:
iPad mini w Retina: $399
iPad mini without Retina: $299.
I wouldn't be surprised if the standard iPad mini also came in one finish (black) or even follow the iPhone's lead with colored cases for kids. I do think they will DROP the price of the standard mini heading into the holiday season, but maintain their brand with a higher-end iPad mini.
II think this is Apple's strategy. It's actually priced "just right". It's not cannibalizing it's flagship, while providing a less expensive option with great margins. What they will do is lower the price or allow retailers to discount more. Overall this puts huge pressure on Android while not tarnishing the Apple brand.