To answer your original question, you're looking at anywhere from $3200-$4200 in a private sale for the non-IS 600 (depending on the condition)... higher end of that range if it's from a shop that deals in used lenses. If you really want to go that route, wait until around Christmas to have a bigger selection... people usually move lots of those (as well as non-IS 400 2.8 and 500 4.5 lenses) right around the holidays.