Whoever gave you that information at Comcast was incorrect.
The average customer pays $0 for their CableCard, because you get free one as part of a digital cable subscription. Additional CableCards run $0 to $3, each, depending on the Comcast division. The $10.75 sounds more like Comcast's cost to buy the card, and what you would have to pay if you lost it; or perhaps that includes the installation fee for a service visit.
When ordering CableCards, it's best to actually go to the local office rather than ordering over the phone. When you order over the phone, they almost always want to schedule an installation. When you go to the local office, you have a good chance of them giving you the cards to install yourself, avoiding a visit from the installer. By going to the local office, you can also better explain what you need -- most CSRs over the phone don't have the training to understand that a single box can support two CableCards. They assume you want two to add two different TVs, and the cost to add programming to one TV is different than the cost to add programming to two TVs.