To be honest, I tend to purchase premixed spices from the Sausage Maker (see web site address below), from whom I also buy both the natural and synthetic casings as well as the cures for smoking and/or drying. I have used their mixes for bratwurst, Polish, beef sticks, chorizo, Italian, and summer sausage and have liked them all. Most of their spice mixes cost $7.99 and will do 50lbs, but details are given for making 10 lbs and 25 lbs, and whatever is leftover keeps forever in the fridge.
http://www.sausagemaker.com/
To be honest, I think if I were to try and buy all of the different spices that go into all of the different mixes, it would end up costing nearly as much as buying them premixed.