Like the Rolex Submariner, the SM58 has been cloned at lower and lower prices since its introduction. The design is solid regardless of the price point. Imitations from Pyle and Audio Technica sound great and cost less, but aren't as rugged.
If you _want_ to spend money for more pleasing tone the Beta 87A from Shure is outstanding. As are similar cardioid microphones from Electro Voice and Neumann