This whole thread bothers me.  The result has to be just like a music
box but it needs to be "improved" in all sorts of ways and it must
be cheap.

I can think of at least a few ways to achieve the goal without cutting
gears or making any complicated or precise mechanical components.  Only
existing mechanisms would be needed plus a simple add-on device, but it
would not be possible for a few dollars or pounds or euros.  The idea is
simple but it would take time to perfect.

Maybe a digital synthesis is what is needed; it doesn't have to be cranked.

Best regards,
Spencer Chase
Garberville, Calif.
http://www.spencerserolls.com/ 

 [ I would ask the customer which is more important: the musical
 [ performance or a shiny, traditional brass movement?  -- Robbie