Thank you all for the responses! I got busy and completely forgot about this thread... Well, I'm back now. I have updated the original post, and upped the max to ~$100 (can go a bit above now), rather than a hard max of $100.
Based on all the comments about microphones built into headphones, I am now planning on getting the mic seperately
So... is there a difference in sound quality between open-air and closed headphones? If not, what is the difference?