Esteemed watch collector,
the value of an Eterna watch can very depending on numerous factors, in particular its working condition, its last service, its general physical condition, its rarity and the prevailing supply and demand for simulair watch styles of the same type.
If you wish you have your watch valued, I am sure you will understand that I am unable to give you a serious and objective answere without beeing in possession of the watch in order to analyze it in detail.
Therefor I recommed that you have your watch examined by a auction house or an antique watch dealer of your choice, who you will know as well as, if not better then me.
For reasons of impartiality, I cannot provide addresses and therefor leave it up to you to make your choice based on your own preference or location.