This is from the Comcast Regional office by me.
Outlet A (Primary) - CableCard #1 $0.00 CableCard #2 $1.50/month equipment fee
Outlet B CableCard #1 $6.95/Digital Access (A/O fee) CableCard #2 $1.50/month equipment fee
One TiVo is either A a primary with no outlet fee and possible second card fee, or B as shown above. One TiVo never gets charges two outlet fees, you are getting ripped off.
If you have no Comcast STB, the charge you should see is only the second card charge ($1.50 -$2.95) I don't know how much exactly.
I have one S3 with two cards like you do, and will scan my latest bill. (Hey, I got that right, first time.)
So you see, The cable outlet is free, one outlet with service (how else can you watch TV, need one outlet) and I only pay for second card, $1.50 in my case. My second TiVo has no cards, I stream to it for high def, Not worth $8.45/mo to get to record more than 2 HD shows at once, TV isn't that good.