I think it's reasonable to pay the actual value of the items, not the absurd markup at low volume places.

Consider an item that sells on average once a year and is bulky. That items is marked way up, and it makes sense given the space it takes up. When you buy it, you pay for the rent to keep one there all the time.

But if you just beak something, there's no way that the store should be entitled to the rent that went into keeping the thing there. That would be an unearned windfall out of nowhere.

If it's due to your own negligence, the fair price would be to compensate for a replacement (including the shopkeep's time to order it, place it on the shelf, etc if that's relevant) plus any reasonable cost to having the merchandise missing while a replacement is ordered (for example if you break something that is a show-piece in the store that draws people in). In normal circumstances though, none of these "extras" apply and the fair amount is basically the cost of the item to the store. At least that's what I think is fair.