What's proper etiquette for someone's 50th Wedding Anniversary?

I'm 22 years old and live in California. My step-grandparents 50th anniversary is coming up, and I'm flying all the way to Virginia for it. Airline tickets are NOT cheap, and I'm going to be staying there with my family for a week. Therefore, I'm sure I'll have to pay for food, etc. My mom wants me to throw in $10 to help get my step-grandparents an anniversary plaque from all the grandkids. When I told her I would get back to her on it, she threw it in my face that they still send me a check for my birthday and Christmas every year. I don't ask them to do this nor do I want them to. I know that $10 is really not a lot of money, but (and seriously not to sound conceited) I feel like it's enough that I'm even GOING to this anniversary party to begin with. My husband is getting out of the Corps soon, and we're trying to save up money. By me even going to this damn thing, that's NOT helping our financial situation. Do people even give gifts for 50ths? I thought it was just the couple that gave each other something, and if they wanted to share their special day with family and friends, so be it. Can someone give me some guidelines or just suggestions on what I should say to my mom or what I should do about the gift? Please and thank you.