A pepper mill grinder can be purchased from places such as: Ikea, Tesco, Asda, Argos, Amazon and Lakeland. They come in a variety of sizes depending on what is needed.
a peppermill
I think you mean a "reel grinder". It is a machine used to sharpen the reels of a mower
Very little. Both take big ones and grind 'em down into smaller ones. In many cases, the internal workings are identical. If I were to be pressed to it, I would say that the main difference is that a salt grinder must be made of stainless steel, where a pepper grinder can be made of mild steel.
Yes. A salt grinder works the same way as a pepper grinder. In a salt grinder you will see salt crystals or sea salt.
In order to minimize the wear rate of steal in a pepper grinder without poisoning the body is to keep the steel pepper grinder from getting wet. If the steel portion of the pepper grinder gets wet it can rust. The grinder can also become clogged by certain types of peppers.
As far as the salt goes, there's no advantage. The salt is the same whether from a grinder or a shaker. For pepper, however, a grinder has an advantage. Fresh ground pepper is much spicier than pre-ground pepper from a shaker.
On Amazon, the prices of an electric pepper grinder vary between 17$ to 134$. The most bought one on Amazon is Ozeri Graviti Pro Electric Pepper Grinder, which costs 25$.
A simple salt grinder can often be found in the spice isle of many supermarkets. More high end type grinders can be found in many department stores, in various styles, many often accompanied by a matching pepper mill.
Someone can purchase a Nutrimill grain mill grinder from a number of companies such as Amazon. Amazon has a large selection of grain mill grinders from a number of manufacturers.
Many people sharpen their drill bits on a grinder. It's tricky to describe how and I'd advise asking an expert to actually show you, or second best, look at some Youtube videos on the subject.
There are many places where one can purchase a salt and pepper grinder. One could try online shops such as Amazon or eBay for deals on salt and pepper grinders.