I'm not familiar with that turntable, so am not sure how good it is. Your money might be better spent on a new cartridge and a phono stage.
If you're using the phono stage on the carver preamp, that is probably a weak link. Something like the Hana SL and a Parks Puffin would be under your budget.
You should also listen to some other subwoofers before adding another Sunfire sub. I had one of their 8" "true subwoofers" a long time ago and it sounded like a little fart box compared to other subs I've owned. Maybe their newer ones are better, but even if they are, a bigger better sub (or multiple subs) will be a lot more "metal" than that little 8" sub.
Unless you want a certain kind of look for your turntable, get one that will sound best with any kind of music. If it will play classical or jazz or hip-hop and sound good, it will sound good with metal.
Some used turntables that fit in your budget and maybe leave some money for a phono stage - Music Hall 5.X or 7.X, or a Clearaudio Emotion or Marantz TT15S1.
As others have mentioned, isolation of the turntable is important if you want to play loud.