For the gun....350$

In my mind, judging by the criteria that was stated it looks like there is two choices.

Bolt action.....Savage 210
Single shot....H&R ulta

Both are tack drivers, the only big difference is that the H&R accomplishes its accuracy with the use of a 10ga barrel. That means even though its a single shot, it is about 10-15% heavier than most rifled 12ga guns.