This is a really difficult project!
7 (powered) degrees of freedom, light weight, low cost, 3kg payload and it has to be "industrial" too?
3kg at the end of an arm might be 100's of kgs of leverage at the shoulder pivot. That would be a hard one to make "lightweight" even for someone with lots of experience, a machine shop AND a large budget.
Maybe you could explain exactly what it has to lift, how far, and how fast, and how much you really want to spend. That might be a good starting point and will decide the basic construction and types of gearmotors etc.