There are Disney photographers located in various locations throughout the Disney parks who will take a picture of your entire family. The first time you use them, you'll receive a Photopass card, which the photographers will scan each time you get a picture taken. There is no charge for this.
When you get home, you log into the Photopass website and view your pictures.
Where the cost comes in is if you want prints of your pictures or if you want all your pictures on a CD. One good thing is that you can add character signatures and Disney borders to the pictures. You can also make greeting cards, a photobook or a photomovie using your pictures.
I believe the cost for the CD is $125 and prints are $12.95 for a 5 x 7 picture and $16.95 for an 8 x 10 picture.
I believe where the discount you refer to was for prints of pictures taken specifically at the
MNSSHP. I don't know if they'll have this deal again this year or not.
Hope this helps.