What is the estimated value of a 1904 Gardone 6.5 caliber bolt action rifle?

You don't give us a lot to work on- but Gardone Val Trompia was, and is, the home of Beretta. Among other firearms, they made different versions of the Italian Army rifle, the 6.5mm Carcano. Value of ANY firearm is dependent on the specific model, and condition. The Carcanos are not especially high dollar collector's guns, and may sell for $100-200. Visit the website for surplusrifle.com for some more information, and see if yours looks like the ones there. As a side note, the 6.5mm Carcano was the rifle reportedly used to assassinate Pres, John Kennedy.