You will do far better by buying a bare drive and a USB3 enclosure (or USB3/SATA dock) and putting things together yourself, than you would do by buying a "pre-packaged" drive.
One of the most important issues is "warranty". Don't you get a much longer warranty period on a "bare drive", than with a pre-assembled unit?
Also, VERY important, is that to get the full speeds an SSD is capable of delivering, you need an enclosure or dock that supports UASP (USB Attached SCSI Protocol).
DO NOT buy a drive, enclosure, or dock UNLESS it is specifically stated that the device supports UASP !!!!!!! (shouting intentional).
Here's an enclosure that supports UASP:
http://www.amazon.com/Optimized-Ina...sr=8-1&keywords=inateck+2.5"+USB3+uasp&dpPl=1
Here's a dock that supports it, as well:
http://www.amazon.com/Optimized-Ina...sr=8-2&keywords=inateck+2.5"+USB3+uasp&dpPl=1
(Disclaimer: no financial interest in either of the above products)
Then, get a "bare drive" from the vendor of your choice. You can keep an eye out for SSD sales at dealmac.com.
Putting the drive into the enclosure is a one-minute operation -- doesn't even use screws.
Putting a drive into a dock is even easier -- can you put bread into a toaster?
Use Disk Utility to initialize the drive to HFS+, journaling enabled.
Then, download either CarbonCopyCloner or SuperDuper and clone the contents of your internal drive to the external.
Then, reboot, and off you go!