Nice find! The bad news is that the 1858-O is one of the commonest dates in Seated halves, so the cleaning and surface porosity will hurt the value quite a bit. It had AU/Unc. details, and I would expect a final price of $40 to $80 if you were to sell it off in an Ebay auction. A certified, no-problem example of this coin in AU-55 could be purchased around $220. The reason the cleaning and porosity hurts the value so much is that collectors have many, many examples of this date from which to choose, so they can be fussy. Many people will not bid on a dug coin.