You’re throwing around a yoyo all the time right? Just do it on the street with a tip jar in front of you. You won’t get tons of money the first time you try it, but the better you get the more you’ll make. If you plan on competing, it will also help a lot with audience engagement and being comfortable on stage.
(Depending on where you live you may need a permit for this kind of activity, so look into that before you get started. )
You could also make and sell your own handmade goods via something like ebay or esty. Yoyo strings, hand carved wooden counterweights, and paracord bracelets are examples where the raw material is cheap, which will make it easier to turn a profit. Your parents might even provide some capital if you show them that you have a clear business plan.
I knew a very poor kid in high school that got into an expensive college, and managed to pay for his 1st semester of tuition by selling musubis and home-made candies at school. There were also people that bought snacks in bulk at costco and sold them for $1-$3 a piece (whereas they paid ~$0.25).