There is a hidden cost to Amazon, and it's the death of our high streets and independent retailers.
As per my comment to the other commenter in the thread, there will of course be times when Amazon makes sense, for more expensive or difficult to source books.
Sometimes, a book may be desperately, urgently needed tomorrow.
Most of the time, the price difference isn't substantial and time isn't of the essence.
I'd rather keep my money in my local economy, rather than subsidising Bezos' next jaunt into space.
And honestly, given America's current behaviour, I'm currently of a mind to avoid sending a cent a across the Atlantic.