Hello Adrian,  Unfortunately we need to know a great deal more about
your musical box before we can even guess at its value.  Your question
is something equivalent to, "I have this old stamp from around 1890.
It's about one inch square and orange.  Seems in good shape.  I think
it's from England.  How much is it worth?"

Much that needs to be known could be discerned by a savvy collector
given the opportunity to assess it in person but just knowing some of
the basic physical facts and a guestimate of quality and operability
by someone not all that familiar with the field is simply inadequate.
I suggest you let people know where you are and perhaps a collector
in your area can give you a hand.

The box is most likely made by Mermod Freres who used the patented
Jacot safety check.  It is probably worth somewhere between $500 and
$5000 but could go off either end of that.

Hope this helps if even a little.

Jim Heyworth