I guess the answer is: it all depends. Are you trying to win the competition or simply use it for the experience? Many young students will use such competitions as a way of testing their own skill level, of getting experience in a competitive environment, and as a way of getting outside professional feedback on their performance abilities.
If the expense of such a competition is something you can tolerate I would certainly consider entering it, even if you don't think you can win. Having said that, I must also point out that I am not a very competitive person. When I enter things like this I never do it to beat someone else, just to do the best I can do.
As with all opinions, your mileage may vary.
Ed