If you've ever wondered how much advertising is worth to a company there's no better measure of that then Kindle's Special Offers.
$249 without Special Offers
$179 with Special Offers
That's $70 they expect to make off of you with advertising, just in the pricing of the device.
That's the hard part about subscription services vs. advertising: advertising pays stupid amounts of money to market to you in the hopes you'll buy shit.
Want to change this? Make advertising a liability.