I have a homenas setup around ur budget... Got a low powered amd processor motherboard combo, a good psu, a 1tb hard drive for starts and a mini itx case...
Mainly for storage, torrent download rig and streaming over wifi (since i do not have my home wired with ethernet)... Able to stream 720p videos on wifi, to my desktop, laptop, tv and plethora of mobile devices....
This uses about 40w power, which is lesser than that of a regular tubelight....
And it runs in Windows server 2012, with plex for media streaming... You can choose any open source NAS software, but i chose windows server, as all my home computers run windows, and its easily compatible with other OS... Also if you attach a monitor and keyboard mouse, it becomes an additional capable windows device for basic computing in some hypothetical emergency situation
Prebuilt NAS consume even less power, but lack expandability, OS choices, and options for cool mini itx cases
