You're not going to get a feature film quality camera for a low price. You can get a 4K home video camera and yes they're really 4K - but resolution is only one factor. There is also compression, the quality of the lens, the quality of the sensor, etc. And that's just the camera. Lighting is hugely important, too.
That said, you can definitely get an affordable camera that shoots a great image. Just don't think that "4K" in and of itself means you're gonna get anything that looks like Hollywood films. If you're just shooting stuff of your family and friends, you'll have a lot of good options.