If possible, buy one off of a fellow smasher, and try and make sure to get one in good condition. Ask if the controller has any issues prior to buying it (you'd be suprised the amount of controllers an average player has that work just fine and are broken in, but don't see play because it isn't as beloved as their main controller). By doing this, you're guarenteed to get a good quality controller that was very likely used by a smasher in tournament in the same condition it is in when you aquire it. You can fairly easily locate smashers in your area that would sell you a controller through your local facebook account.

As for the importance of the condition of the controller: Both games require precise inputs in order to compete. If, say, Zero has a controller with a shitty A button that has lag between when it is pressed and the action appears on screen, do you think he would still be able to win every tourny he attended prior to MLG? And in Melee, would hax be able to double-shine-grab if his joystick was wonky and didn't input the downward directon accurately? The answer is easily no. Even at a beginner level, if you start learning, especially from the very start, that your B button have 5 frames of lag between when it is pressed and when the action is displayed in-game is what is supposed to happen, you're gonna have a bad time when you inevitably attempt to switch controllers or when you're trying to correctly punish a read, etc etc. It'll be bad and you'll be sad, so may as well make sure that doesn't happen from the very beginning.

Additionally, I don't know who you want to play in Melee, but especially if you want to play Fox or Falco, learning any good, complex tech will be really difficult.