LG's popular 27-inch 4K IPS monitor (the 27UD58-B model) is currently on sale over at Amazon. This is priced at $291.40 right now, which is a great price, considering the regular price is $449, making it a really great deal for those that are looking to upgrade their monitor setup at their desk right now.
This monitor from LG is a typical 16:9 aspect ratio, and not the widescreen model that LG is pretty popular for as well. But it is a pretty good quality 4K monitor from LG that does also support FreeSync, which makes it a really great monitor for those that are gamers. LG has included two HDMI ports here as well as a DisplayPort, so no matter what laptop or computer you have, you'll be able to easily plug it into this monitor. And you can even plug in a gaming console in the other port to get some gaming done when the boss isn't looking. This monitor isn't anything fancy, which is why it's under $300 right now. But if you are looking to get a 4K monitor, this is likely the cheapest one available right now, considering most 4K monitors are north of $400 - even when they are on "sale" - so you won't want to pass this one up. It's definitely going to get the job done.
This item is also eligible for Amazon Prime's free shipping. Which includes free two-day shipping, and pretty cheap (usually $3.99) next-day shipping if you need it extra fast. If you are not an Amazon Prime member yet, you can sign up for a free trial of Amazon Prime. You'll get 30 days free (if you're a student, you get 6 months), and then it's $119/year (or $59/year for students). Prime members do get a whole lot more than just free shipping though, so be sure to check out the full benefits.