You're being told the truth. The worth of any rifle lies not only in its condition but also in its rarity. Your grandfather's rifle, while a very good one, is also very common. Hundreds of thousands of Remington 700s in 7mm Remington Magnum have been made. You can buy a brand-new one for under $400, though admittedly it won't be the BDL grade. Even the BDLs have been upgraded since your grandfather's was made. Today's all have cut checkering, instead of the impressed checkering used in 1965.