A quick estimate, snowy: I'd say students could stand to save at least $0.30 to $0.40 for each dollar spent on textbooks if they went electronic. So, an electronic textbook would cost as low as $60 compared to its $100 paper counterpart. This is a conservative estimate. Paper, distribution, and sales make up most of the savings.
So...would the $489 price tag on the Kindle make it worth it? Probably...especially for a 4-year degree.