If I were going to spend extra cash on this build, I’d buy a 1TB hard-disk drive and a FreeSync monitor. The HDD is currently $50 at Amazon, and you can get a 27-inch Dell IPS 1920×1080 FreeSync monitor at Micro Center for $150. (Some may argue that a 27-inch 19×10 monitor might not have enough pixel density, but I don’t have as much issue with it at this price, especially when I get the joys of variable refresh rates in exchange.) I might even choose to instead go with a dual-channel RAM configuration instead of the cheaper single-channel one for an extra $7. All told, these upgrades would bring the cost of the build to $559, which is still quite good for a complete system.
It’s an opportunity which comes only once a year. If you fail to build your gaming PC now for cheapest rate you can find the year round, that opportunity may not present itself again.