We've been back from our trip for a week now. MIL wants to buy the CD, she already gave us $100 toward it, so I HAVE to purchase it. I'm pretty sure my DH threw away the coupon booklet.
You can look on the Photopass website or the Photopass Facebook page and see if they have any discounts available.
The biggest discount you missed by not doing the pre-purchase, but that ship has sailed. You might find a free shipping offer, or maybe a % off deal (rarer), but I think that's about it.
Depending on how many photos you actually want from your account, it might be cheaper just to order a few digital downloads vs. the whole CD.
I have seen a $15 off coupon code on the photopass website. It is not there all the time, but seems to pop up every couple of weeks. I don't know if it can be combined with the pre-order discount...never tried to do it.
??? Then it's already paid for. The only additional discount you could get at this point on the CD would be free shipping, if they happen to be offering that when you're ready to order.