Depends on what MP level you're farming, I don't see any reason for a Bot to farm at higher levels then MP1. It's the best experience per hour (for me), and you're more then likely be gaining more legends/items due to faster farming speeds, rather then higher MP levels. I've been using Rend build since Level 1 Paragon, now I'm over 60, I felt it was a chance to improve my farming time, and go along with the WW build. I will then view how many items I get per hour on each build and thus, will figure out which is more effective at farming. With 100m budget, you'll probably come out quite well with a Barb which is able to farm MP1, but probably 2-3, however I am sure it'll slow down the rate of farming.
Edit: Item's went up 200 per hour with WW build.