Most livestreamers will tell you that audio quality is a LOT more important than video's. I cannot agree more. You want to make sure that your audience can hear you clearly, even if your image is not the best.
Yeti microphone is affordable, and has high quality. it has different gears that you can adjust for different purposes such as podcasting, live streaming, interview, etc.
I highly recommend Yeti and have been enjoying using it.