I've got a subscription to Audible.com and when I visited the site today, there was a banner sale offer of 3 extra credits for approx. $36.00. The sale is supposed to be good through Oct. 31. You can't normally buy extra credits if you run out of them; they only accrue monthly with your subscription fee.
Just figured I'd mention it for those of you who are also picking up the Liaden books in audio format, since there's a wealth of audiobooks available now.
The Liaden Universe audiobooks