At checkout, enter the code APDI50 to get 50% off the list price for all ticket categories. When you register, there will be a box asking you to “enter a priority code” at the bottom. Enter APDI50 in that box, and be sure to accept the terms of cancellation box just above it.
You will see the actual discount at the last page before paying for it, but don’t sweat it, it will work.
[thumbnail photo credit: flickr / michael_reuter ]