I do cota at mp8 w/ ~50m gold barb. You'll have to go a bit higher if you want to do act 3, but my stats unbuffed are around 600ar, 120kdps, 6000armor, and 46k hp.
I use the whole IK armor set and a skorn. Don't go LS on the skorn, go for AS and as high damage as you can get w/ 180%cd. I also use lacunis w/ crit and a decent vile ward. I didnt even bother w/ trifectas for ammy and rings, just went for higher CC and CD. Use WW build/modify for your bots ai.
This is a very budget build, but i've thrown it together twice now for under 60m and both barbs run cota mp8 with only random deaths. They get great exp/hr out of it too and I'm planning on leaving them there indefinitely to legendary farm.
If you are looking to do key runs or something of the sort, go much higher than what I posted as my stats, probably around 750ar, 7000armor, 55k hp, and 200kdps. But getting this is going to run you well into the hundreds of millions.
