These automated guitars are available from the Ragtime Automated Music company.The Ragtime company continues the tradition of piano-roll player pianos and fairground organs, but using modern technology.MIDI files are used to drive individual solenoids which act as string pluckers and fretters.

A single automated classical guitar costs $12950, an electric bass plus guitar and drums costs $24950. They are intended for use as coin operated novelties or as fairground attractions, but some people install them at home. Peter Jackson, the director of the Lord of The Rings films, has one with 47 percussion instruments, a bass guitar, guitar, banjo, flute pipes, accordion and Piano. Listening to sound samples of the guitar, I can't hear any dynamics in the string plucking, they don't seem to be able to vary the volume of the notes.

Link: The Ragtime automated music company

http://www.youtube.com/watch?v=tlRi77pBYNI