I got a refurb 4k monitor from monoprice a while back for 179.
Works great with my macbook pro’s thunderbolt 3 output.
Make sure your computer can actually output 4k.
HDMI needs to be the 1.4 version or later to do 4k , and 2.0 to do it at 60Hz, ideally you should use displayport or thunderbolt if you want to be sure you can use the higher resolutions at higher refresh rates. Lots of folks have issues with HDMI when they try 4K.
You’ll might find your computer can’t keep up with 4K video unless you have hardware accelerated h264 decoding in your video card.
I have a raspberry pi 4 that supports decoding h264 at 1080, but only does h265 video at 4k, so I need to transcode if I want playback at 4k. It also supports 4k displays at 60p over its HDMI output, but so far I’ve only gotten my monitor to do 30Hz on HDMI.