Depending on what you need lets say for video playback, you might be fine with something like Haswell comes to NUC
, it shoudl consume very low power (check the review), it should also be very small, you still need to buy ssd, memory and wifi i believe. If you are worried about the fan being like a laptop, or if you want also a storage 2.5 hdd, there are custom cases for it like Akasa Tesla H Fanless Solid Aluminum NUC Case - VESA Mountable (A-NUC05-A1B)
. There are options from Gigabyte aswell, BRIX
There is also options if you want a more standard Pentium/Celeron/i3, like building around Antec 110
, just grab your prefer mini itx mobo, memory (standard or low profile) 2.5 SSD and 2.5 hdd and you should be set. There are also options like H3 Plex
for fanless setup if you wish, there are other models and manufactures, this is just an example.