Conversation so far:
What type of guitars did Fred Frith play?
Fred Frith has used a Gibson ES-345, an old 1961 solid body Burns, a modified 1936 Gibson K-11, and a homemade six- and eight-string double-neck guitar.
Was there anything interesting about Fred Frith's playing technique?
In a typical solo improvising concert, Fred Frith would lay a couple of his homemade guitars flat on a table and play them with a collection of found objects.
Has Fred Frith influenced anyone to use his technique of laying guitars flat and using different objects to play them?
In 1999, Fred Frith was appointed the Luther B. Marchant Professor of Composition in the Music Department at Mills, where he currently teaches composition, contemporary performance, and improvisation.
Is there anything else interesting about Fed Frith's guitars?
In Fred Frith's early table-top guitar solo performances, he used a homemade six- and eight-string double-neck guitar created by a friend, Charles Fletcher.
Is the six- and eight-string double neck guitar that Charles Fletcher created for Fred Frith expensive?
Fletcher constructed the six- and eight-string double-neck guitar mainly out of old pieces from other guitars that Fred Frith had. For the body he used an old door.

Question: What have his guitars sold for?
Self-contained rewrite: What have Fred Frith's guitars sold for?