This is what you get for going to a commercially-run con. They are EMPHATICALLY money-making enterprises, and you should expect to get charged for any opportunity to get near guests of honor.
At fan-run cons the GOH's tend to be much more approachable, because they don't accept unless they're willing to actually interact with the fans, and there generally isn't a fee for the signature line. Of course depending on whose signature you're trying to get that may not be an option.
(Personally, I don't need star signatures. There are a few author signatures I've accumulated... but I value much more the chance to have heard them speak, and in some cases to have spoken with them, and in a few cases to have socialized with them.)