Recently SDL announced the release of SDL Trados Studio 2017. You can buy the latest version of SDL Trados Studio through the SDL Transaltionzone Store.
The price is relatively higher compared than other CAT (Computer Aided Translation) tools.
If you buy it cheap, you will be able to wait for the Black Friday Event (or Year End Event or something) or the Summer Discount Event (if any). For example, this summer, SDL held an event when they offered 40% discount for SDL Trados Studio 2014.
I think SDL will a special offer sooner or later.
Anther way to buy Trados cheaply is to use a group buy event at Proz.com.
I noticed that a group buy event which provides 40% off on SDL Trados Studio 2015 ended. Such event will take place from time to time.