Don't know WHERE you are?! In Thailand those HDD's quite a long time available. Acer was starting about 2 years ago with those 2.5" external HDD's and WD even before Acer! And there other brands as well! SAeems to be that you'll need to take some time for to go to IT-M alls etc. for to get updated what the Market has in them shelfs!
The Acer 500GB USB 3.0 2.5" cost in Thailand THB 1,380.00 which is app. US$ 43.00!! Seems to be really bad at Best Buy! What a name!!