First I do not have an XBox so this may not be helpful at all. But I recently bought the Ultimate Edition Abyssea online for $20. If you go to the main playonline page (www.playonline.com) there is a "Buy it now" button at the top left of the page and links to several different places you can buy it.

The add-ons, if purchased separately, are $9.99 each. Not sure if maybe this is the price you saw. Anyways like I said, I'm not sure if this is helpful, but I hope it is! Good Luck!