You'll kill me but I picked up a Mesa Boogie Dual-Rectifier head for 500$ US. XD Best amp head I've ever played out of, and great for metal. Guttural, throaty sort of tone.
But on that train of thought, have you considered looking into used equipment? You may be able to find some epic deals like I did (pure luck).
I also know that Line 6 has some heads for under 500$ US or so, but not sure if they would really give the sound that you're looking for.
My thoughts: try used Sorry I wasn't much more help. Good luck tho!