Depends a lot on whether you want to sell it, or whether you want to make some money. Generally, if you were commissioned to do the work, it's a penny a stitch, plus all materials. But from everything I hear, people rarely get their money's worth on something like that because people don't value XS the way the needleartist does.

I sell little stuff at holiday craft sales once in a blue moon. But...theres no money in it. If you figure out the time it took you to do it....you loose money. Lately I have been saving to give as gifts to those who truly appreciate all that went into the project

Very little market, alas. Charge by the st (1c or 2c if there are tricky threads) or by the finished piece. Price is btw you and buyer. You might try selling on eBay.
mb

I have never tried to sell anything I made, but I would imagine you need to be aware of any copyright restrictions on selling if you didn't design the picture yourself.