Providing you go about this in the correct manner, you can have good success in getting backstage passes. However, if you do this in the wrong way, then you'll probably need to find money from somewhere because you're going to have to buy a ticket in order to get in to see your concert.
The good news is that you will find several resources which can help you get backstage passes. One resource is a free ebook offered by ConcertGroove. Although it's an introduction to the topic, it could be if the idea of backstage passes is new to you.
Also, if you really desire your Christina Aguilera concert ticket without it costing anything i.e. with a backstage pass, you might try Google and taking a look at what other resources you can find.
There's no doubt that possessing a backstage pass is exciting. Not only can you see your concert, you may also find that you can get really close to your favorite star.