The Apple Thunderbolt Display is really two devices in one.
mentioned above, for one thing you're getting the screen - which is a color accurate 27" IPS 2560x1440 panel.
The second device is the Thunderbolt dock. When it was first released, the Apple Thunderbolt Display was one of a kind. Companies like Belkin, OWC and Elgato have since released standalone dock devices, which offer similar functionality. The key benefit is that by connecting one Thunderbolt cable from your computer to the dock/display you can transmit video, usb, ethernet and firewire. The Thunderbolt Display has several of these ports on the back.
So, in answer to your question: if you're looking to the Apple Thunderbolt Display for its accuracy, then the price is competitive for a color-accurate IPS 27" 2560x1440 panel (such as those from NEC or LG).
If color accuracy is not a primary concern, then you might consider cheaper panels, in conjunction with a standalone Thunderbolt Dock.
I have owned a Thunderbolt Display for the past few years, and find it a crucial component to my setup and workflow. I can highly recommend it.
For what it's worth - I believe the Apple Thunderbolt Display has recently been discontinued by Apple, indicating there may be a newer version to be released, likely incorporating the forthcoming Thunderbolt 3 standard.