In 1876 a telephone costed approximately $20.
About Alexander Graham Bell
Bell was born in Edinburgh, Scotland on March 3, 1847. While trying to perfect a method for carrying multiple messages on a single wire, he heard the sound of a plucked spring along 60 feet of wire in a Boston electrical shop. Hearing the sound, Bell believed that he could solve the problem of sending a human voice over a wire. He figured out how to transmit a simple current first, and received a patent for that invention on March 7, 1876. Five days later, he transmitted actual speech. Sitting in one room, he spoke into the phone to his assistant in another room, saying the now famous words: "Mr. Watson, come here. I need you." The telephone patent is one of the most valuable patents ever issued.
The purpose of the telephone was to be able to communicate with people without being in the same room. This would be much faster then sending handwritten letters.