There are a lot of different places you can learn from and do research. I just got an issue of Barrel Horse news and it has a barrel horse prospect section in it. I think the best thing you can do is find a mentor that is experienced who you can go to for help and to learn from.
I agree that it seems like the best way to go is find a horse that is at least already started on barrels and is in your price range. Or find an older finished horse that is a little less expensive. If you put a lot of time into your research you can find some good deals occasionally. Networking is always a great way to find a horse that isn't being advertised for sale as well. I think that Fallon Taylor seems to sell some horses that would be very reasonable in price and experienced on dynastyequine.com .
I understand that it is hard to not be defensive when you get advice that may be harsh or not what you want to hear, but I try to always remind myself that in life the wisest and most experienced person knows that they don't know everything and can always learn more. The person who knows the least thinks they know everything. Being humble when receiving advice is a great thing to practice.
I wish you all the best!!!