Typically you can get a used version for at or a little above the ebook price... But with a paper copy you get to resell it after the class is over so you usually get at least 50% back.
But there are times when the convenience would cover the cost... Some textbooks are rentable too, which is cheaper. Amazon offers some for 30 bucks for 60 days. (Hint, you can use your iPad to take pictures of each page, then make a pdf out of them.... then you'll have a permanent copy).
So it just depends on how much you'd like the convenience. A lot of the most expensive ebooks are also the largest and most cumbersome (aka the ones that would be great to just have on your iPad).
But there are times when the convenience would cover the cost... Some textbooks are rentable too, which is cheaper. Amazon offers some for 30 bucks for 60 days. (Hint, you can use your iPad to take pictures of each page, then make a pdf out of them.... then you'll have a permanent copy).
So it just depends on how much you'd like the convenience. A lot of the most expensive ebooks are also the largest and most cumbersome (aka the ones that would be great to just have on your iPad).