This isn't limited to travel-oriented sites either. I went to Lens.com the other day to price-shop some contacts, and my price at checkout (right where you're putting in your payment info) was something like $15 more than in my cart! Even accounting for taxes. It was still an okay price relatively speaking, but I immediately left, because there's no way I'm rewarding that behavior.
Of course, I then got the "you left something in your cart" email.