How do you figure the value of an item stolen?

Baylor v. Commonwealth:

If there is no market for a used item (in this case catalytic converters) then the value of a replacement cannot be used to prove value. Value must be proven by another means and must be the value of the item at the time it was stolen. Possible methods offered are:

[T]estimony of a lay person as to the property’s fair market value, the opinion of an expert, or by traditional accounting principles, starting with the original cost of the item and then factoring in depreciation or appreciation.

Of course, the question becomes, if there is no market for the item once used and the value is the value when stolen after it has been used, is there any value if it's not the cost of replacement?