Barrelbeginner, I'm a little worried about hearing this from you. The only reason is, is that you've said that your goal is to become a professional barrel racer. I'm going to be blunt here- if you want that to be reality, eventually- maybe not today, next month, or next year, but eventually you will need lessons to accomplish that, and probably a horse that costs more than $500 as well.
I have nothing against people who don't take lessons, but if being a professional rider is your dream, you'll need to learn from someone with more experience from you.
The difference in my riding from switching from a sub-par instructor to a good instructor is huge. I wouldn't want to know what my riding would look like if I didn't ride with an instructor! (Not saying you're a bad rider, more poking fun at myself and trying to make a point).
Are lessons expensive? Most of the time. Are they worth it? Yes.