UHD monitors are not very cheap. And when you're talking above 27", you're proportionately increasing cost. It won't be long before the cost comes down, but people are still trying to grasp what HD & 1080p really means. This is an advantage for manufacturers right now, so inflating the cost of UHD monitors is quite easy.
You're probably bugged by why 27" has the same resolution as a 19" HD monitor. You'll find the same thing with a 70" TV. HD is the current viewing standard, so manufacturers aren't heavily looking towards anything higher. You'll find higher resolution systems are typically used for people working with high end graphics, or large format images. Putting together multiple screens is an option, but in the world of graphics, the bezel of the monitor hinders the overall image. The larger the image and the denser the pixels, the larger the file.
So what does this all mean? The larger the file, the more bandwidth is consumed. With framerates of video in a progressive format, it taxes the network infrastructure in enormous amounts. Video Cards, processors, memory, storage, etc. have all evolved to handle bandwidth issues. What hasn't evolved is network infrastructure. Broadband companies aren't sure how they need to upgrade their infrastructure, and wait until the last minute because of the expense. Instead they oversubscribe to cover these costs. They don't have to oversubscribe, but they aren't going to let their profits get cut, either.
So how does this affect UHD monitors. Since UHD monitors aren't the primary concern, and a 50" monitor looks fairly clear in 1080p when the 27" is super sharp at the same resolution, because it's pixels are smaller......people really don't care to more purchasing into UHD monitors. This means manufacturers are going to limit the sales, and mark the cost up until the standard changes. At that time, you'll probably see 70" 1080p TVs sell for about $300-$400 because of high surplus, and low demand.
As an alternative, you might want to consider paying less for a HD monitor at 1920x1080. or consider the ASUS, as mentioned above.