Right now, Ultra HD monitors are out of most consumers' reach as they are priced too high. 4K-capable displays range from nearly $1000 to close to $5000, depending on what you are after.
NPD DisplaySearch is now reporting that the industry will ship around 2 million Ultra HD monitors by the end of the year, with display makers paving the way for "affordable" 4K monitors at around 28 inches by the middle of the year. Normally cheap means crap quality, but Samsung and LG are both diving into the "affordable" 4K race, which should have users excited.
So if you're in the market for a monitor with a massive 3840x2160 resolution, you might want to wait a few more months as there should be more monitors to choose from.