I think there's a bung thingy on the block, just above the oil filter, as he says. The drainage bung for the cooling system is on the other side of the block though, so I dunno what this other one would be for, but if it's just a plug, then I wouldn't imagine much. Unless you're saying that there is a hole around the plug? If the plug itself is damaged, but removeable, i'm sure you'd have change from a $20.
Can you take a pic? It's possible that someone with experience knows exactly what you're talking about, but I can't picture it.