While true, it is extremely unlikely one would be audited due to a donation of a small amount of household goods.
The cost basis is simple: what did you pay for the item? If you paid $100 for a shirt last month and donated it, unworn, to the local thrift store who will sell it for $50, the cost basis is $100 and the thrift store value will be $50. You donated $50 worth of goods.
If the donated item was a gift from your mom, what did mom pay for it?
The only time it gets tricky is with vehicles, fine arts, collectibles, instruments, jewelry and coins.
