The Antminer S9 sounds like your best bet, but they are currently ~2000 USD per + the cost of a PSU and other little things like cabling and cooling might be needed. They are the most effecient, pulling ~1300w each @ ~12ths.
I would say S7 instead, we have european sellers on the forum selling
Antminer S7 Batch 5 (1210W) + IBM 1300W PSU
total 0.65 BTC fminer+ 90 euro from PSU + shipping costs
that is 4.73 th/s for 3.6kwh he can have 14.2 th/s for 1,275 usd +298.36 usd for 3 psu.
$1573 (14.2th/s ) > 2000$ + PSU 12th/s
He has free power, efficiency doesn't matter