If you already have the bitz - I've seen Dreggs made out of pretty much all GWs Empire sprues, notably Flagellants and Archers. For a more deformed look Skaven or eben Gnoblars. When it comes to metal miniatures my personal favourite alternative is Quasimarty the hunchback dwarf be Heresy:
I have two sinister looking minis that I painted from Reaper that I would recommend to check out. i believe they are called Dreg Butchers on the Reaper site. You can also check them out on the second page of my humble gallery in the miniatures section. Good luck.