Mixing large volumes of sausage has always been troublesome, for the home DIY sausage maker. I broke down and bought one of the large mixers, from Cabela's. They say it holds 44 pounds of meat. Yeah, right
It will hold 44#, but it won't mix it very good. 25# is a good size for it, and mixes it nicely. Even 35# was almost too much for it.
I have always been on the lookout for mixers. We had a nice 100# mixer, when I worked at the grocery store, 20+ years ago. The only ones I see now, cost $2000
, and go up from there. I wish I would have had my head screwed on right, back when my father closed the store. I should have "acquired" the mixer, and a few other items from the sausage/meat dept..
As far as making one, I guess you could do it. I would try to find a stainless steel 35 gallon drum, to start with. Then you would have to get a motor, a center shaft (S.S. also) and some other S.S. plates, to make the mixing paddles, and deflectors. Then you would need to TIG weld them together, and inside the drum base, so they wouldn't hit each other, but be placed so when the inner shaft turned, it would push the meat around and mix it.
No wonder they are so expensive.