One of our favorite 4K monitors is on sale right now, with the Acer XB280HK available at Newegg for $599, down from its normal price of $899. The Acer XB280HK is a 28-inch 4K monitor that has NVIDIA's G-Sync technology built-in, with our review available right here.
Sure, it's a TN-based panel and not IPS, but for $599 you're getting a silky-smooth 4K monitor if you have the VGA chops to get there. 4K 60FPS isn't too hard these days with a mix of Medium/High details in most games, with Grand Theft Auto V able to hit 4K 60FPS on something like a GeForce GTX 970 without a problem.
You'll need the following promo code "EMCARKW22", which is available until April 22, so get in quick. The code only works for those who are signed up to Newegg's newsletter, so you'll need to sign up for that if you haven't already. If you're already signed up for it, you would've received the e-mail alerting you to the sale, but if you've missed that e-mail, consider this your notice.