With current market price for ETH, a 6 rig investment will yield you a net profit of $655 per 30 day period, when every gpu is able to push out 30mhash/900mhash dual mining. Your investment for said rig will be anywhere between $1800-2300 depending on where you buy your parts.
pre-built rigs are great if you want to pay $100-500 extra to save yourself a few hours of price comparison/assembling. Nvidia doesn't even come close to AMD when it comes to mining ETH/DCR.
I beg to differ on nvidia.
Mining an older algo; with 5x 1080 and 1x 1070; over 1K/mo in earnings. thats not chump change in comparison.. better wattage/hash ratio too.
my equivalent of 3x 1070, earns me over 300/mo presently.
see for yourself:
http://zpool.ca/?address=1PHSDYvVp6HpqtuUPocK41DrdeHbbezaePhttp://zpool.ca/?address=1kLsGT9egk3utSKZH46ydTbKj5oMnmBoN