Sale of Inherited Goods

We inherited a warehouse full of my mother-in-law's possessions.  We are paying rent at a storage unit because of the sheer volume of stuff. The goods cost us nothing but we have warehousing costs, which are not deductible unless we claim a value for the inventory.  There are thousands of pieces in this inventory.  There is no way we could determine a value for this stuff.  We have been selling off pieces a little at a time and know how much we have received but are under water with the warehousing costs. I'd like to be able to deduct them. Any suggestions?