I have to agree with dannthr here. Audio equipment, generally (there are exceptions) doesn't really depreciate in value, especially if its good quality. Depending on the style of music and your own unique voice will determine how good a microphone will be for you. If you have no idea about where to start, start with a dynamic mic like a SM58. If you're really wanting to keep on budget, go for the PG58. I use the PG57 for my guitar work and if you use the mic correctly, it will take a real audio hotshot to point out its not an SM57.
If you fancy going for a condenser microphone, then I'd definitely reccommend Rode's NT1A. You can even buy it bundled with a pop-shield. Its around £100 so....$150-170 I'd guess. Most of Rode's microphones are fantastic for their price and the quality is top notch. They even have lifetime guarantees!