Advice please...

I am invited to a wedding in a different state that I used to live in…the wedding is at the end of summer… I found out that they're having it at a restaurant. So I was planning on giving 100 bucks totalling 200 for my husband and I. Is that enough these days?? I'm going based off of venue and friendship plus the fact that I am flying in but I'm always flying into that state so I can't not give anything. I never had a wedding so I didn't receive a gift from them or any gifts in general so I don't really have an idea...