Trying to find the value of this 1974 Yamaha TX500

[krager]

Hello,
  Im trying to figure out the value of this ( http://homepage.mac.com/bradranola/PhotoAlbum1.html
 ) 1975 Yamaha TX500 because the guy wants to trade for my 1975 914 Porsche that is non-running and needs work.  Please let me know what you think its value is and if you know where i can look these kind of things up.

Thank You,
Kevin
KRagerUCI@Yahoo.com or KFro@surf.co.nz