Anywhere from $100 for one in rough shape to $500 or more for one in mint condition. One like you describe should be in the $250 to $400 range. Closer to the bottom of the range if it has cracks in the butt stock or is loose at the take-down joint between the receiver and the barrel/mag assembly.
If it's tight, no rust or pitting (polished down to bare metal from use or brown patina is okay), no bad gouges in the metal, no cracks or serious gouges in the wood, and the bore's free of bulges, dents or pitting, then it'll be closer to the $400 mark.
To get more than that, it would need to have the majority of the blueing still intact and the wood in mint shape. There were comparatively few of the trap models and the trench guns made compared to the field models, so they can command a significant premium, with the usual caveats for condition.
Add an extra 100 bucks to all these prices for 16 ga.
