I bought my 1990 TransAm with a 350 TPI motor for $1500!
For what I see in the pic I would say $400-$500, add a hundred or so if theres a complete harness and ECU.
There should be a price differential for it being the lesser 305 but at this level it's all about what you want to spend and what he'll sell for but I bet he'll never move it for $1500, thet'll get you a complete LT1 swap or a basic LS1 long block easily. Bith are stronger and more desireable motors.
The engine code is LB9 by the way, L98 for the 350 TPI.