Well you've got the right mindset!
It's great you've got realistic goals. I wish more people had that. With what you want to achieve, I think you could do it yourself. Keep going to the local jackpots as much as you can and observe/talk to people. Who knows. You might even be able to find a trainer that way, by word of mouth.
Also try to get your hands on as many resources as you can. There are a handful of free barrel racing videos on YouTube (Sherry Cervi, Martha Josey, and Dena Kirkpatrick, are a few to mention). But also get your hands on books and DVDs if you can. More knowledge = more knowledge.
You'll want a horse that's at least 4 years old and either has a good solid foundation of general riding, or that you could put that on yourself. You need to be able to stop softly from any gait, back easily, sidepass and move on the diagonal, simple and flying lead changes, turns on the fore and the hauchnes, neck and direct rein, etc. Basically, be able to move your horse's body in any way you choose, at any speed, at any time. THEN you can start patterning on the barrels.
You'll want to walk or trot the barrels (no galloping) for at least a few months. In barrel racing training, slower is better. If you go too fast too soon, you'll create bad habits. Also, you don't have to drill them with the pattern. You don't want to do it so often that they become sour on it and resent it. Working on the pattern 3 or 4 times a week is enough, in my opinion. And if they do something perfect and correct, great! Quit on a good note, even if it was only trotting through the pattern once.
And the local jackpots are a great place to do exhibitions and get your horse used to the hustle and bustle.
∞•*˚ Βгįťţαňγ ˚*•∞
It is not enough to know how to ride; one must know how to fall.