If I get the Kindle with Special Offers can I upgrade to disable the ads? Would it cost more than just buying a Kindle without Special Offers?
From Amazon's help on Special Offers:
Unsubscribe from Special Offers
You can unsubscribe from Special Offers on your Kindle if you do not want to receive Sponsored Screensavers and Special Offers.
Amazon is able to offer Kindle models at a subsidized price by delivering Special Offers and Sponsored Screensavers. If you originally purchased a Kindle Special Offer Device you will be charged a one-time payment to unsubscribe from this service.
Last I checked, the one-time payment that was listed for me was the same as the original amount I saved by buying a With-Special-Offers device.