One of the worst habits you can develop as a magician is buying tricks that you don't need or will perform. Especially when in today's market, a single trick can cost at least 20 dollars. It's best to master the material you have and polish it into a good routine. But if you have to buy something, buying magic books will get you the best bang for your buck. A used copy of a Tarbell volume or Scarne on Cards costs around only 15 dollars, but it's chockful of tricks. Even if you only find 3 or 4 tricks worth learning, you've gotten more value than the 20 dollar single trick.