According to widely circulated data from the coverage of The Alman Brothers suit against Sony BMG, you could expect something like $45 of each thousand songs sold to be paid to you in royalties. That's around 4% of the amount paid to Apple for your work, and around 5.7% of what was paid to the label. For The Almans', that works out to $24,000 when taking Nielsen SoundScan data of 538,000 Almans' songs sold as downloads since mid-2002. I don't have SoundScan data on your sales, but I'm sure you do. So the labels and Apple got 96% and you got %4. And as you said, there were no packaging, shipping or storage costs for your album sold though iTunes.