Gift for Host Family

Hi all!

I am a college student staying with relatives this summer who are letting me stay for free, which I appreciate greatly (they refused to charge me any rent, as a relative). As the summer is almost up, I wanted to express my gratitude to them for being hospitable hosts and including me in their family activities; I have already expressed my gratitude in some ways through treating their children to many things (did my expenses and realized I've spent over $500 on them) but I want to do something more---I am thinking of buying flowers and a cake before I leave. I am thinking of purchasing something a bit less temporary (going to keep the flowers probably). My budget is around $100 but I can go a little over. Any ideas?