I believe this is a rifle not a gun. Go back and look again for the model number. I think you are giving the serial number and that doesn't help.
Crosman owns Benjamin air rifles. they offer a service to locate repair shops the repair older Benjamin rifles See the link below
Around $50
What condition is it in. That determines the value
The Benjamin model 342 ( Currently owned by Crosman Airgun Co) was made between 1969 - 92. In fair working condition it is worth between $50-$70.
It would be worth around $55 in Excellent condition.
It would help if you stated the model and the condition of the pellet gun. Without some information it is not possible to answer you.
What model is it. How old is it, what condition is it in, is it still working?
What Condition is it in? That determines the value.
What Model and what condition is it in?
The Benjamin 720 was made from 1947-1962. In good condition it would be worth around $80 to $105
What condition is it in. That determines the value.
It would help if you stated the condition of the rifle.