Inventory valuation for ebay sales

I set up a small ebay business to sell miscellaneous items that we already owned (think garage sale).  I had enough sales last year to need to file a Schedule C.  How do I account for the valuation of that initial inventory on Schedule C.  I bought and/or was gifted everything for sale; however, I don't have proof of purchase for any of it.   Do I put an estimated value in the "value at the beginning of the year" box?    Ditto for the valuation of the inventory at the end of the year.   

I'm good with how to handle anything I may buy with the intent to resell -- just not sure how to account for the stuff that been gathering dust in the basement all these years.

thx