How much would it cost to cover up a bald spot the size of a quarter?

I currently have relatively long hair, about 3-4 inches long. However, I am going to be joining the military soon and you as you all already may know, you get a nice shave. I really don't want to have my bald spot showing. When I was younger I hit my head on a concrete floor after falling about 5 feet. The bald spot occurred because there was a wound there and I picked the scab which then tore the hair out. Injections did not promote growth. Also, do I call a dermatologist or something directly?