If you are a high schooler competing with other high schoolers, I wouldn't worry about the trailers, tack etc. that the other kids have. They only have it because of their parent's money. It's fine and good that their parents help them if they can, and that's also not to say that they haven't worked hard with their horses. As a few have mentioned, some of those kids with the expensive trailers and tack could even eventually come to be your friends, they probably aren't paying as much attention to your gear as you think they are, and the ones who are paying attention and judging you in any way for it aren't people worth knowing in the first place.
Your uncle sounds like a toxic person if that's what he's telling a teenager. And he's wrong. Rodeo is a big sport now but all those skills on horseback originated from a working-class world in the beginning. The "rich" people weren't the one using horses to work with cattle, out riding ranches, etc.
I am not interested in participating in competition of any kind, I'm a little late to the game for that as I didn't start riding until I was an adult. But I definitely feel the wage divide in horse circles and in all other aspects of life here in Kentucky. I was from a family that didn't have much but we always had what we needed. Mom actually gave up keeping horses on our land for a long time because she simply didn't have the financial means nor the time to do so. My dad is still in debt and if anything that has taught me never to spend above my means if I can help it. I do have some student loan debt but without it I wouldn't have the career I do now. Rather than be ashamed of my lack of money I'm pretty proud of my budgeting skills and household management. I just acquired my first decent-paying full time job a few months ago and at 26 years old I don't have enough money to my name to even think about buying a horse trailer let-alone a vehicle that would haul one. But my bills are all getting paid, I'm bringing down my student loan balance, and am able to save money back in my savings every month while being able to afford the care for my horse and the training I need for myself. All my tack is hand-me downs and the horse was a give-away by someone who was moving and couldn't keep her, and that person got her from the pound (so I will be paying for my lack of experience and her training.)
Having to work for what you have now and having to think about how you will manage your resources may seem stressful now, but it will be beneficial to you in the future I think. You'll know how to manage your money when you get out of highschool in a way that some of the other high schoolers you compete with may not.
"She could be a witch, and he would never build a pyre upon which to burn her thoughts, desires and dreams."