As everyone has pointed out, you're better off if you buy good brushes. However, don't get rid of your el cheapo brushes because you are occasionaly going to have to do something with a paint brush that will damage or destroy it (certain methods of applying a finish, applying liquid glue etc) and the cheap brushes work great for this (and doesn't break the bank).
I would also make the suggestion that when you buy your brushes, see if you can also get some brush soap. It will remove any paint the thinner and rag method of cleaning doesn't get (you'll be amazed at how much paint remains). It also conditions and softens the brushes and keeps them usuable for a longer period. Grumbacher has a pint jar of the stuff for somewhere around 5 bucks and it lasts forever (I bought mine at an art supply store about 15 years ago and still have more than half of it).
Finally, storage. If you're like me, you're going to end up with a bunch of high dollar brushes laying around and you want to keep them usuable for as long as you can. Don't toss them int a box or drawer (you will shorten the usuable life). The ideal way to store them is to suspend them vertically with the point down - but if you have more than a couple of brushes finding the space and the method to do this can cause problems. I store mine vertically with the point up in a couple of beer steins I got when I was in college (back during the Middle Ages as it were). One stein is for my good brushes and the other is for the el cheapo ones. A friend of mine who is into oil painting hot glued some small Pringles cans to a piece of cheap paneling (about a foot long and a couple of inches wider than the cans - keeps the cans from tipping over) and uses that to store his brushes in.