Mics for documentaries

This should be good enough for you. Or, you know... It's a school project so you could just use your iPhone's mic and the teacher probably won't care

Well if you're using the iPhone then get audacity and file converter. Also, you can use Sony Vegas trial for the editing part :P. Just record, and convert the file into mp3 then remove noise and other crap in Audacity. Last, mute the video and use the edited audio instead in Sony Vegas

I'll do the voice work for you. I sound like Sean Bean. No really, I do.

Go to a pawn shop or a used video game store and get a Rockband microphone (see avatar, LOL). Doesn't matter if it says 360, PS3, or Wii, as long as it's USB. You can plug it into your computer, and it will "just work," at least it does in Windows 7. Not sure about OS X and Linux. And it's a pretty good microphone. There are better ones, obviously, and it will matter if the mic is gently used or beat all to hell (so if you can get a deal on a brand new one, better), but for quality:price it's a good buy. Works better than those little cheap mic-jack mics you can get. Now finding a mic stand, that's another story.

I wouldn't even record on a smartphone, but I don't think it matters. They all use pretty crappy mics. Even if you have a decent Bluetooth and route the audio through that, it isn't going to be any better.

I am using this (just without the switch) for my amateur music recordings and it was about 20 €. I get clean sound with it but then again it's not just plugged into my PC. This was just to show you don't have to spend much money to get clean sound. But since it's just for school I wouldn't advice you to buy a mic just for this. Try to use what you have and as it was stated before try to reduce noise with audacity. If the teacher expects you to buy a mic for this maybe you should have a talk with him. If he doesn't listen to you talk to someone he has to listen to. The quality of your work shouldn't be valued by your mic.