Kinda hard not to when some people have to pay their own way to BronyCon. I don't know how to say it any more kindly, but your parents/guardians cannot and will not pay for everything forever.
Sorry to say, but there's little else a 13-year-old can do for cash short of chores. Prime-season for lemonade is about ending (at least in the East Coast US). Argueably, you could sell Hot Chocolate, but that's also implying you'd have the time for it.
The one other thing I could suggest is, if your state supports it, is recycling bottles and cans for cash. It's some rank and time-consuming hard work, but it is as fast as you want to make it. You aid your community while doing this as well.