What was the original price?
Beside asking about the chamber, I would also ask the gunsmith about the condition of the inlet, what the trigger pull was like and if it was a factory trigger or something else.
From a bargaining standpoint, figure out exactly what the stock is and if it fits you right but tell the pawn shop you're buying it for parts.
If they still won't budge on price, offer to buy it without the barrel for $100 less than your previous offer.
The point of doing that isn't to buy it without a barrel, it's to make them think the barrel has no value to you. They probably won't want to try selling a used Remage barrel so they might move a little on price.
The biggest thing to understand is the longer you drag this out, the more chance that it gets sold to someone else so pick a price that is the maximum you would be happy to pay and know if you try to bargain for a lower price, the time that takes is all risk.
Good luck.