Depends on what level you want to show. For county fair steers, you can go out and buy them, but look at the economics and what you are trying to teach your kid. We have spent a little, not a lot of money on some nicer heifers that my kid owns. Have AI'd them to easier calving Angus and clubbies for the first calf and after 2 years he now has a string of 2 bred cows, 1 bred heifer (last year's show heifer) and 1 open show heifer. The winnings at some smaller jackpots have about knocked the price of the show heifers down to market price. This year he will show at county fair one of the calves he raised. Probably won't be a contender, but he only has about $600 in the calf (what he could have sold him by the pound for this fall). That calf should sell for somewhere around $2000 at county fair. Even if he bought all the feed (which he doesn't), he would still clear a profit. He had another calf that was a dud, so sold him at market price and used the proceeds toward a second show steer. Should about break even on the second steer and could do a little better. Trying to teach him how to run it like a business and this is his college saving plan.
If you want to teach them how to gamble, then buy the expensive ones and try to hit the grand at jackpot shows or your county fair. However, the upside potential is way less than the risk of losing a grand or two buying something. Our philosophy is to make money at this even if it doesn't pay much. We aren't interested in gambling with the college saving plan, but probably won't see the fancy banners very often either.