First, there is no requirement for any gift of any value when you attend a wedding. The gift is not payment-in-kind for the per person cost fo the reception. Secondly, what it costs you to attend or whether or not you are a guest or a member of the bridal party is not the issue -- really -- although this seems to be a bone on contention for you.
The only consideration in giving a gift is what you feel comfortable spending based on your financial situation and how close you are to the bride and or groom. If you are all just out of college, struggling with loan debt, and not making much money, you shouldn't spend a loan payment on a gift. If you are financially comfortable and either member of the couple is a dear and long-time friend, you'd want to spend more.