vocals on built-in mic?

[japes]

I'm doing some recording with multitrack and have been forced (due to my almost-zero disposable income at the moment) to forego trying to get a fancy mic. While the built-in mic and the headset mic both work pretty decently with the guitar, I just haven't been able to get a very good sound out of them for vocals. Any tips on getting the best sound I can out of the limited resources I have available? Alternatively, are there any decent mic options for under $20?