the PSU they already have,
they don't have a psu, they buy in bulk what they need
calculating an 4th miner put in function 2 months ago is ~600$
They get those psu directly, they are custom made for them and they are probably pretty cheap as a 1400w server psu can be individually bought at ~200$
http://www.newegg.com/Product/Product.aspx?Item=N82E16817377050 To get 4TH we talking a lot more power and standard home outlets don't allow over 1800w so unless this is JUST for data centers we won't see a 2kw home miner s6.
.4 watts a gh = 6000gh done if they want to do it.