They also seem to jack up the price if you have been looking at an item for too long. To plot Amazon prices vs time, you can use camelcamelcamel. camelcamelcamel is an Amazon price tracker. That can help you determine if the price is at a long term high or low, or a local max or min. Used to be more fully featured, but is still a useful website.
Have often found that Amazon is NOT the lowest cost, including shipping. Sometimes they are. Have to be a savvy shopper, or you will be burned. Kind of like most things these days - got to look out for yourself, because no one else will do it for you.