Don -- I would say that $650 is an excellent buy for you.  (In fact,
I'd say ANY organette of any type that is fully functional is worth at
least this much.  See the end of my post.)  I'm assuming this is the
20-note instrument, similar to the Symphonian, with wooden tracker bar,
that plays small rolls using a pneumatic action inside the windchest.

Last year I paid quite a bit more for such an instrument, recently
restored, with 12 rolls.  Maybe too much, but it is one instrument that
I can just sit and crank rolls through and enjoy the music.  The arrange-
ments are very well done and quickly make you forget the 20-note limit.
Recut rolls are available.

There should be one or more lids that you can use as volume and tone
controls.

At least two makers built similar instruments with compatible rolls,
although the pin ends may differ slightly.  Some models run the roll
left to right, others front to back (and all upside-down to a player
pianist :-)

Some used three single-ended feeder bellows in a fun-to-watch miniature
of a ship's engine room, while mine has two double (French) feeders
90 degrees apart.

Before you buy, run a careful listening test on the bellows: Play a
roll with sustained notes, and see whether the rhythm is modulated by
your crank turning.  Many organettes with leaky bellows (needing
recovering) will accent the music as each feeder goes through its stroke,
and put a "rest" in the music between strokes.  If you can play at a
slow tempo without these extraneous accents, you have a great
instrument.  Otherwise, recovering the bellows is a bit of work.

Even with some work needed, $650 is not bad, but you could talk him
down to $600 or less.

Mike Knudsen