You are pretty much dead on for the low sale price of $469 retail, based on the disti cost I can see at this moment in time.From a strict budget point of view, AMD currently is the best option. (unless the i3 quad core K is a crazy value like I am picturing in my mind).
Anyway, 6 core vs 6 core. The i7-8700K is going to walk over AMD.
However if you have a strict budget and require a 6C/12T CPU. AMD will always win. Price delta would hypothetically mean a i7 + GTX 1060 setup vs Ryzen + GTX1080 setup
Oh and assuming no price gouging and going with typical markups, the i7-8700K should be below $500, but not by much.
"Could" be as low as $469 at retail. But with the word of low stock until 2018, be prepared to pay a lot more I guess :<