OK, wow - what a broad question. It's kinda like asking:
"How much is my camaro worth? It's in good condition."
Ok, well what make and model is it, what year, define "good condition". Does it have factory paint, matching engine block, original upholstry? Has any of that been redone? If so, how well?
See what I'm getting at?
Good quality photographs of the rifle, all serial numbers, stock markings and a reliable description of the bore would give us somewhere to start.
Alternately, I could answer as follows:
"Anywhere from $150 to $2000, it depends."