Not sure why you are saying this is better from Fandango. I see codes for 20% off. A 3D movie is $13.50 so that would be $10.80. The $7 Costco ticket + 3.50 upcharge would be $10.50.
Are you getting Fandango codes much cheaper somewhere? Just not sure of what you are trying to say.
Fandango also charges fees