In my experience the must cost effective way is aparment complex offices are always willing to share in their news letter to tenant. Community colleges at least here in Georgia. Job trade shows in colleges. Age gruop is very diverse. Community trailer park also a great source. Middle age single parent in need of additional  source of imcome, they tend to stay longer, be responsable and loyal because is about helping their families. This only work if the building for wish you are hiring is near any of this facilities, when not I use Indeed.com or Hispanic news paper and or association.