I noticed some people already use this PSU, but I don't think I've seen reference to this one that comes with everything you need.
$85 plus $14 shipping
Title:
GPU Mining Power Supply Kit: HP 1200 watt 80+ gold PSU, Breakout Board, (8) PCI-E power plugs, (4) 24in PCI-E 6pin to 6pin cable set, (4) 24in PCI-E 6pin to 6pin + 2 cable set
Description:
HP 1200 watt 80+ gold PSU / PCI-E Cable set
100volt - 240volt AC compatible
Can power (4) Radeon R9 390
Designed for 24/7 mining operation
http://www.newegg.com/Product/Product.aspx?Item=9SIA7GT4RD5414&cm_re=r9_390-_-9SIA7GT4RD5414-_-Product
(I have no affiliation with the company, just passing it on)
$85 plus $14 shipping
Title:
GPU Mining Power Supply Kit: HP 1200 watt 80+ gold PSU, Breakout Board, (8) PCI-E power plugs, (4) 24in PCI-E 6pin to 6pin cable set, (4) 24in PCI-E 6pin to 6pin + 2 cable set
Description:
HP 1200 watt 80+ gold PSU / PCI-E Cable set
100volt - 240volt AC compatible
Can power (4) Radeon R9 390
Designed for 24/7 mining operation
http://www.newegg.com/Product/Product.aspx?Item=9SIA7GT4RD5414&cm_re=r9_390-_-9SIA7GT4RD5414-_-Product
(I have no affiliation with the company, just passing it on)