How much do you charge for distribution?

It can vary, but usually it’s about 20-30% of the net revenue generated from the sales of the audiobooks.  (After the retailer has taken their cut.)  For instance, if your audiobook was selling for $20 and the retailer took a 40% cut ($8), your net revenue would be $12.  Open Book Audio would take a 20% cut of that amount ($2.40), and you would be left with the remainder: $9.60.