Heya Tyler, first up...the best two ways of enlarging your fan base is passive - you sit back and let people findo your videos themselves, sounds silly but it works well. Or you can create facebook page and twitter, tell your firends to follow and then they'll tell their friends. (This one can be a little embarrassing)
Next Up...If you want to do commentaries, the best mic you can get for around £40-£50 is a Behringer-C1 Condeser Mic. It provides excellent sound quality but will require 'Phantom power' (You will need a mixer as well). If you want a USB mic, I would suggest the 'Blue Snowball'. It costs around £70 but is USB powered and provides an also exceptional sound quality. The final option really would be an external recorder 'Zoom H1' for around £70. This provides good sound quality but also allows you to record without using your computer so you could use it for filming as well. It allows you to copy the file to the PC and edit it normally and you can plug an external mic into it to replace the Stereo Mic's built in. I would prefer the Blue Snowball as it is the easiest to use and will provide great sound quality. If you want something more profesional, get a Behringer C-1 and a mixer or if you want portability, use a Zoom H1.
I hope I answered you're question, if I did, please like this otherwise feel free to PM me.