Amazon often costs 5 cents less and you might find that all the issues of Bocci the Rock are at Amazon and one is missing from Walmart, but Walmart is taking the fight to them.
For photography stuff in particular, I buy from B&H, Adorama or direct from vendors such as Red River Paper. Often the prices are better than Amazon and the service is much better (e.g. the owner of the later has schooled me on details of papers and printing that most people couldn't imagine)
[1] Not against giving the tip, just against saying I don't like the comparison against free shipping from other vendors.