It's not as simple as just a mic. What do you have in the way of an audio interface? Do we have to budget for that as well? You have to get the sound from the mic into your computer.
If you are talking about a VO mic, just a VO mic and nothing but a VO mic in the $300 range, and you have everything else that you need (stand, shock-mount, pop-filter, mic pre, audio interface) here's a selection:
Audio-Technica AT4040 - $300
Audix CX112 - $300
sE Electronics sE2200a - $300
Rode NT1000 - $330
Blue Microphones Bluebird - $300
AKG C3000 - $250
The mic alone is not enough, you need to work on your mic technique.