USB microphone for christmas gift?

My girlfriend is really talented singer but were both dirt poor and she doesn't have money for a good microphone. I had a friend help me get some really professional beat maker software for her pc and I am going to give it to her for xmas but I don't what kind of microphone to get her for her pc that will allow her voice to sound the same when it comes out on the pc. I am poor and can really only afford like a 100$ max for a microphone can somebody please reccomend a good microphone for me to get my girlfriend for xmas, I would really appreciate it because she sounds so beautifull when she sings and she writes her own songs.