Max Charitable Contribution for a single item

What is the maximum amount allowed for a single item to give to a charity?  I saw that if something is over $5000 it requires an appraisal, but if it is a single item, do I need an appraisal if it is over $500?  We donated a brand new King Mattress that we bought for $999 (plus tax), so I don't know if it will require me to get the new mattress appraised, if the receipt will work, or if I don't need any of it since it is under $5000.


Thoughts?