From a certain point of view the SKS is more valuable; yours I take it.
Can your son, in general and wherever he happens to be located, walk around with the SKS slung across his back in public to defend himself with if the need should arise?
If it's the dead of night, someone breaks into your house, and you have to grab your child and hold a firearm with your other hand, which would you prefer, the SKS or a pistol?
For the average American civilian who is not engaged in land warfare as part of a late 1940's Warsaw Pact army, a pistol is probably a bit more useful.
If the SKS was in good condition, I probably would have sold the SKS and then used the money to purchase a pistol but this is your son we're talking about and the PT-109 may have been exactly what he wanted.