Mu budget is 300 dollars.
Quite a few $30 – $60 webcams have better audio than the overpriced and gimmicky supposed-high-quality microphones that are advertised for $100 – $300.
A large majority of those just have standard cheap electret condenser capsules (similar to those in mikes sold for $1 – $20) but with "electret" omitted from the description to get people to confuse them with true condenser mikes.
A decent gaming headset microphone is probably similar quality.
Or, try something like this:
It's a standard electret mike, with USB interface, at a sensible price.
If you want seriously high quality gear, then either a Shure SM58 or MXL V67g microphone plus a USB Audio interface, eg.
The Yetti microphone by Blue Mic. They have a few other ones but that's the best from what I've heard. I think it's a USB one though. From what I remember I think you have just enough for it. Most mid range microphones cost $250
check out sony products. they are great for such things