Charlotte, when we originally researched for this post, they did indeed have the free shipping offer. It may be a recent change in policy. Are you actually with the company or a customer?

First: For some reason History books have very high prices.
who thinks I want to pay 60 dollars for a book.
Are they text books, ok, there is no way of searching for history books that are not text books at high prices. not to mention people who sell used, still charge 40 or more . . .
The sites you listed, the compare prices: It is not as if those sites look at local book dealers everywhere. Amazon, the problem there is prime, if you are not a prime, then shipping and tax, only a few sites show that, so the book is at least 4 – 5 more than shown on the list. Only one shows in a pop up window shipping cost. Best way to buy inexpensive books is . . . search, and again, etc. Maybe at some point you get lucky. Some one made a comment once that was a waste of time. . . guess they don’t mind what they pay. I go with 3 sites mostly 5 sites in general. Navel an Military Press has really great prices, the shipping is bit much, however if buy three or four at once you still save. Blackwell has some good prices, Wondery the same, cept they are low stock as I write this.
To find the best price, keep searching.