Don't be browbeaten by the hecklers. $20 is a great price, especially when you have a captive audience. Hell, I'd hock it for $30!
Selling is just a matter of setting expectations. $20 isn't much diff from $10. Couple of hamburgers and a shake. Start talking fast...
"It's true that cost is higher than the generic charger cables you can buy at Walmart. But these specialized cables are only made in limited numbers and thus have high per unit cost for us. As you can see below, wholesale cost for the Asus TF700 charger cable is $15.33/qty1. Our pogo-pin charging cable has more components and thus costs more to make."