DONATIONS TO CHARITY

I'm donation a piece of family heirloom furniture to a non profit.  TT is asking me for the purchase price and I have no records.  The item is valued between 2500 and 4500 (I'm getting an appraisal).  What do I put down for cost?  If I put zero it doesn't allow me to deduct anything.  The piece clearly has value so can I not simply deduct the appraised value?  If so then how do I fill out the part where it's asking for cost?