The price on Amazon moves up and down, seemingly randomly. See the various links in previous posts, for them and other sellers that might have good deals in your part of the world.
What's certain is that the publisher will give you 20% off (of the $79.99 in the USA or the £ 54.99 in the UK, if you use the code LYON2017 at checkout, through 2017. But there will be some shipping cost and tax, so compare. Let us know what you find, and please do review it wherever you buy it.