i'm about a year away from graduating with a degree in audio production, so take my advice or leave it, but it's solid advice...
please don't ever use the mic on your camera and expect professional quality sound. mics on cameras are complete crap. they're literally put there so people won't complain about it not being there- they serve no practical purpose as the sound is so bad, it's unusable 90% of the time.
if you want to get a decent shotgun- and want to use it CORRECTLY- look towards getting a boom set-up. any mic you mount on your camera is going to limit you to the point where you might as well be cutting off your balls. Sennheiser makes some really quality shotguns that aren't going to fuck your wallet over.
just please, don't use your camera's mic... it's so, so bad.