Maybe increasing a little bit the budget you can get good hardware, please read this awesome article http://1stminingrig.com/best-mining-rig-hardware-mine-2017/

Be sure that some stuff isn't available because the mining is getting trending and people are trying to buy everywhere where they see GPUs

The hash rate goes from 21 - 29 Mh/s so  * 6 = $674 - $930 monthly (without calculating electricity).