Totally worth it.
And I'm betting that if you make up a decent enough sponsorship package, you could end up making money. It's all in the art of begging for money and it starts with the sponsorship package.
Make a breakdown of costs, write a bio, write a blurb about how important this trip is and how the company would be supporting a young athlete and write something on "What is Equestrian Sport?". Use the words sport, high performance, athlete, opportunity, important (and synonyms), etc.. A LOT. You cannot overuse these words. And pictures of you riding in comps are also a bonus.
Once you have a 3-4 page document, fire it off to a lot of companies in your area. If there's a mom-and-pop store you are in a lot, drop it off there, tack shops, feed stores, etc.. are a good bet too. I like to get my packages professionally printed (at least the front page) and in colour. Hit up people at your barn, your parent's friends (this is a gold mine), etc.
It is actually ridiculously easy to raise money for big trips like this.