The IRS doesn't give directions to this other than the quote below. The FMV, for ease of description, is what it would sell for. It would have obviously sold for more, before it was damaged. The cost out of pocket is not what they are looking for, although it could help you estimate.

Fair market value. 

FMV is the price for which you could sell your property to a willing buyer, when neither of you has to sell or buy and both of you know all the relevant facts. When filling out Form 4684, you need to know the FMV of the property immediately before and immediately after the disaster, casualty, or theft.

https://www.irs.gov/publications/p584