Neutering generally will calm them down a bit, as will age. It also stops or reduces marking behaviors, prevents them from getting a female pregnant, usually stops humping, eliminates testicular cancer, and much more. In general, I think neutering your male makes for a better pet.
Cost can vary greatly depending on where you live and/or where you get the surgery done. I got Jackson neutered for $65 a low-cost spay clinic but I've seen some people pay up to $500 when you add in all the pain meds, pre-op bloodwork, etc.