I worked out a dozen designs on paper before settling on this one as both cheap and practical.
Looks were secondary although it did turn out quite nice.
I took some T-Track and dadoed into the top of side rails making it long enough to rise above 5 manuals.
Then I carved wooden fixtures to hold some aluminum angle stock and to make the clamp bolts stand up straight. Finally I screwed a plastic music rack to the aluminum angle.
To adjust I just loosen both thumb screws, slide to where I want, and then tighten the screws.
It can adjust down to just above the first manual or up to above the fifth manual.
It also easily removed when not needed.
Hopefully you can see pictures here:
"Pipe Organ Adjustable Music Rack"
http://www.picturetrail.com/gid24794024If not then please email me for them.