you can definitely get more than 1lb of cannabis extracted with a gal of ethanol. if you’ve got a centrifuge, you can perhaps get 5 or even 10lb extracted. you won’t have a full gal of ethanol when you’re done, and you definitely won’t have gotten ALL the cannabinoids.
whether or not this approach is viable in your situation is about balancing the cost of solvent recovery and the leaving behind of cannabinoids. In House analytics make it much easier to figure out where the sweet spot is for your opperation.