The current price is $60 (down from $65 in 2007). You can buy it by telephoning Disney, and that used to be the only way to get it, hence the 13 month thing because they had to mail it out....but now you can purchase it at any Guest Services and not have to worry about whether it will arrive before you leave (unlike AP's a DDE card costs $25 to replace!!!).
You can get a second card for $25 (hence the reason it costs to replace otherwise everyone would "lose" their card). BUT...if you and your spouse always dine together, there is no real reason to get a second card. If you typically each go off on your own, then it might make sense.
If you always get an AP, then obviously the timing of the DDE doesn't really matter.....but if you renew it every other year, you may want to consider waiting to get the DDE so that it matches up with your AP, since you must show both the DDE card and the AP to use it. In other words, if you get your AP in January and then wait until June to get the DDE, your AP will expire in January and unless you renew you won't be able to use the last 6 months of your DDE card. Hope that makes sense.