Just curious what the going rate for these are. Also, besides being drilled and tapped on the rear bridge or for a side mount scope, what else would lower values? Thanks.

Anything that drills into the metal is a killer. A cut stock or poorly refinished stock also detracts from value.

Another item that need's to be checked on a Hornet is the chamber. Many 54's and 70's were opened up to a "K Hornet". Many were restamped on the barrel accordingly, many were not. I always carry a K Hornet case in my gun show tool's to try in chamber before a purchase. Once bought a 22 Hornet M70 carbine only to get home and find it was a K.Fortunately, I knew the seller and he refunded my purchase price. They were often opened up to a 222 Remington also, but this is usually obvious.
Steve