live mic trouble

[Puzzle]

Okay, so here's my problem. Right now I'm using a Shure SM57 into a Fender acoustasonic amplifier. I can get away with not plugging my guitar in if I'm playing just a guitar/vocal song, because my guitar projects well enough to be picked up by the mic. However, if I decide to play any instrumentals, I'd much rather the guitar be plugged in to make up the difference. Really, any larger show requires me to have the guitar plugged in, but then my vocals aren't loud enough because the guitar to voice ratio becomes 1.5:1, and I lose the ability to hear myself sing.

Basically, I need advice on what kind of mic to purchase. I'm looking for something $50-$100 that will pick up my voice without picking up a guitar. Also, if possible something that would let me position the mic in front of acoustic or electric guitar amplifiers, since I don't use any monitors (and wouldn't be able to in some venues, such as coffee shops that put me in a corner window where space is at a premium and I already have an amp, two guitars, and a keyboard.) Having to stand 5 feet back from the amp doesn't really help a whole lot.

I'll be honest, I'm a fanboy for vintage-looking mics, so would this: http://www.musiciansfriend.com/product/Nady-PCM200-Classic-Dynamic-Mic?sku=277520
suit my purposes at all?


thanks much
-ay

[Aus_rock_god]

Hang on, run that by me again. Do you need a microphone for your vocals, or for your amp????

[Puzzle]

for vocals, but if possible one that can be placed in front of an amp without feedback or picking up the amp over the vocals.

[Aus_rock_god]

An SM58 is your best bet. If you're sitting in front of your amplifier, your body will absorb the sound.

Don't panic dude, $100 says that you won't hear your amp significantly through the vocal mic.