You can get both trips on one CD, but you'll need to time things correctly. You have 30 days from when the photo is taken to upload it and 30 days from when you upload to order the CD.
If your first
Disneyland day is Oct 18, you should have until November 17 to enter your card(s) online. I would probably upload on November 16, just to be sure. Then you'll have 30 days from then to order the CD - so approximately December 15. I wouldn't upload any earlier than November 16, because you'll want a few days to add borders, etc. to your December photos before ordering.
There is no pre-purchase discount for the Disneyland CD. However, there is a bonus CD that you can purchase and get free shipping (and a discount if you're an AP holder, which I'm guessing you are if you're making two trips that close together). Here is the link to that thread:
http://www.disboards.com/showthread.php?t=2576990
