Shin Sung ?

1550499796_7991843225c6abfd4974d15.75780665_7F3C7A78-630C-4999-A8A5-20B8FAA1A6A6.jpeg

 
That particular model is a favorite of mine in a fairly large collection of nice air rifles. Value is subjective, though . If it is unmodified , it's difficult to shoot and loud. Many of us prefer unmodified for reasons of poor work quality so that can be a value or not depending on outlook . The most I've seen one advertised for is $575 and I believe I've seen them in the $350 range. However , yours is a gen II and I'm not sure of the ones advertised. The early ones like that were incredibly accurate consistently .

Are you intending to sell or buy? 

Bob