to be honest i prefer the old 6 rig setup with asrock h81 pro btc

with $500 you have a rig of six gpu

with the next gen gpu that consume less the perfect setup would be this for six gpu

asrock h81 pro btc
g.skill 8GB
G1840(you may buy a pentium here for only $10 more, it may be worth it for the extra cache ram)
ssd 64GB(120GB i've found one sandisk for only 40 euro on amazon)
evga 1k g2

total is 450 euro + 50 for riser you have your rig for only 500, then you just add your gpu

1kw is enough for future gpu because polaris and pascal will consume something like 120w per card, for gpu like 490 or 1070