[Stupe the Second Sacker]

This has probably been discussed here previously, but I did search and couldn't find. I'm wondering how people determine the cost basis of a card (or any item) bought in a lot. If I buy a collection of 10,000 cards for $1000 dollars, then sell one card for $500 and keep the rest, is the cost basis of that card 10 cents?

Similarly, what is an acceptable way to determine cost basis for cards which you have no buying records of (most of my collection)? Surely, many here have crossed this bridge.

PS...Sorry for bringing the dreaded tax topic up, but there's a lot of people out there who will be trying to figure this out for the first time this year. If not interested, please scroll on.