Normally, AMD's second best Ryzen CPU would set you back just under $490 from a local retailer sans shipping. So being able to grab a Ryzen 1700X for $390 is a very good deal indeed.
It's a 25% deal currently available through Amazon direct, which means you'll have to wait a couple of weeks for shipping if you want the cheapest available option. That'll give you some spare time to grab an aftermarket cooler to go with your new CPU, as the 1700X doesn't come with a cooler (unlike the Ryzen 1700).
There's a 25% discount on the Ryzen 1700 as well, but it's only a few dollars cheaper than the 1700X and not actually a bargain at all, post-currency conversion.
So the 1700X is the way to go. If you really want to save your pennies, you can save around $60 on the Ryzen 1600X from Amazon as well. But the 1700X is the biggest bargain of the lot, and a solid all-rounder to build a new system around.
Update: While the dollar figure at the checkout works out to be about a $100 discount, zombiejesus below correctly pointed out that fees for international bank transfers crimp the discount a bit. See below for more details, and thanks for calling it out.