110$ Mini-ITX Form factor cube case: http://www.newegg.com/Product/Product.aspx?Item=N82E16811112265
120$ Low power mbd: http://www.newegg.com/Product/Product.aspx?Item=N82E16813121401 – review @ http://www.servethehome.com/intel-boxdh57jg-h57-mini-itx-motherboard-review/
135$ 35w(lowest i could find) sandy bridge 2.5Ghz cpu   http://www.newegg.com/Product/Product.aspx?Item=N82E16819116394&Tpk=i3-2100t
78$ 8gigs ram, cheap http://www.newegg.com/Product/Product.aspx?Item=N82E16820226095
hard drive, ($$$$, can go much cheaper here depending on storage needs) – 4 of these in raid 5, 5.33TB actual: http://www.newegg.com/Product/Product.aspx?Item=N82E16822136579R
those drives are 6.1watts idle, 9.6w active: http://www.pcworld.idg.com.au/review/servers_storage/western-digital/re4_wd2003fyys/319493
61$ power supply – http://www.newegg.com/Product/Product.aspx?Item=N82E16817104073

25w: motherboard
35w: cpu
40w max load, 6-10wX4: hard drives(4)
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100w