and if you do take everyone's advice (which you should strongly consider) you can buy an epiphone valve junior head for $100. it's a class A 5Watter (if that means anything to you), just plug it into a cab and turn it all the way up (or whatever your desired sound is). It's no metal amp, but multitracking is a wonderful thing. And either way; good sound and a good mic (at least a 57) will at least get you started. Remember, it's not supposed to sound great the first (10000) time(s) you do it...
So, why try to spend hours/days/weeks/months/whatever trying to find the 'right' sound??? If you're just demo-ing metal material, why don't you focus on just getting reasonable sounds that get the job done so you can hear what the song sounds like recorded before you spend $$$ to do it at a decent place... First of all, you'll save yourself a never ending headache (cause you'll never find "THE PERFECT TONE") and you'll learn more by trial and error... the more you try, the more you {censored} up, the better you get. get it?