What's the easiest or cheapest Ascended backpiece?

I've found it particularly straight-forward to get ascended pieces in all slots. All slots except the back.

Weapons    Crafting                      
Armor      Crafting                      
AccessoriesLaurels or Guild Commendations
Rings      Laurel Merchant or BUY-4373   
Amulet     Laurel Merchant               
Back       ????                          

There appear to be many different options for back pieces, however, their acquisition methods seems to be varied, with some taking more effort than others.

If my primary interest is to get an Ascended back piece, what is the easiest option?