If I can offer some advice, just grab a dynamic. LDC's are not mandatory for great sounding, big vocals. Thom Yorke, Michael Jackson, Stevie Wonder all did fine without one.
Get a 58. If that's too expensive, go with a cheaper handheld. Alot of the rip offs get pretty close for the cash. At any rate the time, especialy with singing, is so much better put into getting the vocal performance right that if you capture it you've won.
However if you want a seriously nice microphone a Beyerdynamic M201 is an absolute motherchugger. Great on vocals where the singer has alot of presence, really just takes in what's being sent and doesn't mess with it. If you're made of cash, I'd go a step futher and say an RE20. If you were dead set on a Condensor I'd recommend the JM47, as that's the best bang for buck condensor I've heard.
Protip: I almost always set up an SM58 dead centre on the singer and if it sucks (and I don't have anything else) I'll swap set up another mic in a less conventional position and use it as a dummy mic- the singer has a physical cue to work off of, and I can toy with mic placement without them having to sing with the microphone 30 degrees off to the right or whatever. Sometimes I've to remind myself they're not a guitar or a drum or something.