the sm57 is good, i used it a lot a long time ago, but even a cheap condenser mic will do miracles... no need for a neumann for 8,000 dollars.... i paid about 200 for mine, a chinese no-brand thing..... i would check out the budget choices, but mics are personal things, what sounds good for one voice might not suit another. From what i hear on your recordings, a large diaphragm condenser mic is all you lack
you'll need phantom power and perhaps work a little on the acoustic environment where you record (i've tied a towel around the back of my mic to avoid it picking up the room acoustics too much
), so it's not an instant solution, but so worth the investement....