I did some research on this topic myself awhile back. I had been using an old blade coffee grinder but, somehow, spices had crept into the area where the blade spins and it seized up. In the course of my research, I learned that "burr" grinders are generally preferred because they tend to produce a more uniform grind than blade grinders. With that in mind, I bought a cheap Mr. Coffee burr grinder at Walmart and dedicated it to spices. It works great. It has a selector for the size of the grind, so you can grind spices coarsely or finely.
One thing I don't like is the burr grinder can be a pain to clean. The part that stays in the machine can't be submerged in water so I use a can of compressed air to blow it out after using it
minimalist home accessories.