Haha, you could be surprised how far you can go with 13$ :P

First, listen to that:
http://www.newgrounds.com/portal/view /590285

The quality is going to be better if you follow that.

You could use an auto-tune too, if you use FL there's one called Pitcher. Inform yourself, that's an easy good sounding thing. You could use an auto-tuned track as a reference too, signing while listening to it, it can help alot

Lastly, general tips for the voice recording (NG is awesome, right?)
http://www.newgrounds.com/wiki/creato r-resources/voice-recording

Good luck!!