The 57 and 58 are not the same microphone.
The 57 is a great studio mic that can be used on anything from amps to toms. The 58 shouldn't even be near a studio, unless you need a scratch vocal track -- it's designed as a live vocal mic. The mid-range and presence are boosted through a 58 to help the vocal cut through a live mix (which serves its purpose, but sounds terrible on a studio recording). The 57 has a flatter frequency response and also captures a fuller low end (there's supposed to be about a 10Hz difference on the low ends of the two mics, too).
If you want a cheap vocal mic, I recommend checking out a reasonably priced condensor like a Studio Projects C1 or an Oktava MK series.