garfy is right: you will get plenty of opinions about amps. You will also get plenty of opinions about "metal"
which can mean many different things (and tones) to many different people.
If there are particular bands/artists you like, then you can find out what kinds of amps they use, and while those amps probably cost more than USD 300-400, at least you can then start to look for budget options that will get you in the ballpark.
Another issue is: what do you want to do with this amp. If you just want to play along with your favorite tracks at home, I would have to question whether an amp is the best solution these days. Honestly, if you're listening in headphones, you can just use AmpliTube
and you can get a fair selection of metal-worthy amp models for less than USD 300. If you don't want to use headphones, you can get some monitor speakers (like IKM's iLouds) and make some noise at home.
If you want to go along to rehearse or gig with people, then although people
do do this with AmpliTube, I confess that having a good ol' physical plug-in-and-go practice amp is still pretty convenient. I've heard good things about the Boss Katana-100 MkII, which is a solid-state combo with lots of versatile options and that is supposed to sound good. To go another way, the Orange Micro Dark is an actual 20w tube amp (though probably still enough for a rehearsal or small gig. It's cheaper than the Boss Katana combo, but only a head, so you'd need to put the remaining extra money saved into a little 1x12 speaker cab or something. Alternatively, Orange's solid-state "Crush" amp combos are supposed to be good if you want to go that way, and they are cheaper, too (if less effect-laden) than the Boss Katana.
Honestly, we could just go on and on and on.
But I do think it comes down to what kinds of tones you want and then what you want to do with those tones.