I don't know how much Rockband mics are, but for something that came with a game it sure isn't that bad imo. Could probably find someone who would either sell it to you (or give to you).
Edit:
The RockBand 1 & 2 mics aren't that bad. They also have built-in pop filters.
Au Contraire....
The rockband mic is USB, so it actually works on the PC (take it from me, I use one for recording, cause I'm cheap)
Don't believe me. This is what it sounds like...(fyi only the vocals were recording using the mic, the instruments are computer generated) Yevrag35's Music | Ultimate-Guitar.Com
Trust Starzz.
very little distortion on this mic however it does pick up sound a bit to well, frequently my friends complain that they can hear my mother playing her flute, which she plays downstairs and yet it still gets picked up
but yeah, £11 on amazon! tis really good Trust Starzz Microphone: Amazon.co.uk: Computers & Accessories