Fred Frith has used a number of different guitars, including homemade instruments, over the years, depending on the type of music he is playing. For the more structured and refined music he has often used a Gibson ES-345, for example on his solo album, Gravity. For the heavier "rock" sound, as in Massacre, he has used an old 1961 solid body Burns guitar, created by the British craftsman Jim Burns. On his landmark Guitar Solos album, Frith used a modified 1936 Gibson K-11 guitar (q.v. for details).  For Frith's early unstructured music, as with Henry Kaiser on With Friends Like These, and his early table-top guitar solo performances, he used a homemade six- and eight-string double-neck guitar created by a friend, Charles Fletcher. Frith told DownBeat magazine in 1983: "It was the one and only guitar that he ever built ... he constructed it mainly out of old pieces from other guitars that I had, and for the body I think he used an old door." The possibilities offered by homemade instruments prompted Frith to start creating his own guitars, basically slabs of wood on which he mounted a pickup, a bridge, and strings stretched over metal screws. "The basic design of the instrument is supposed to be as rudimentary and flexible as possible," Frith said, "so I can use an electric drill to bore holes into the body of it to achieve certain sounds ... ."  Frith uses a variety of implements to play guitar, from traditional guitar picks to violin bows, drum sticks, egg beaters, paint brushes, lengths of metal chain, and other found objects. Frith remarked: "It's more to do with my interest in found objects and the use of certain kinds of textures which have an effect on the string ... the difference between the touch of stone, the touch of glass, the touch of wood, the touch of paper - those kinds of basic elements that you're using against the surface of the strings which produce different sounds."  In a typical solo improvising concert, Frith would lay a couple of his homemade guitars flat on a table and play them with a collection of found objects (varying from concert to concert). He would drop objects, like ball bearings, dried beans, and rice on the strings while stroking, scraping, and hitting them with whatever was on hand. Later he added a live sampler to his on-stage equipment, which he controlled with pedals. The sampler enabled him to dynamically capture and loop guitar sounds, over which he would capture and loop new sounds, and so on, until he had a bed of repeated patterns on top of which he would then begin his solo performance.

Answer this question "What has his guitars sold for?" by extracting the answer from the text above.