It used to be out of stock, but currently back in stock with 10+ stock available.
This model has the higher CPU frequency Intel Quad Core (2.3GHz rather than 1.8GHz on the lower end model) with 2016 standard - 4GB RAM, very good price for the specs IMO (with Antutu around 46,000 to 50,000 score) as well as above-average camera and 3000 mah battery.
Full Specs:
http://www.gsmarena.com/asus_zenfone_2_ze551ml-6917.php
Original CTECHIE eBay 20% off deal post
1.35% cashback from Cashrewards
Mod Edit: Price after cashback (commission-refunds) removed from title. Cashback tracking, approval and payments are not guaranteed, and not all users are aware on how to take advantage of such commission-refund schemes.
I used this phone for couple months and its really good. One thing that i really hate about it is the screen quality is really poor compare to those expensive phone(Iphone 5s-Galaxy s5). Battery life is OK but dont expect much if you are heavy user. High specs but cheap quality, you get what you pay.