Although there are some great sounding 2x12 open backs (
my Road King kicks ass), I have to agree about the 4x12 closed back sounding more "metal", and if you are going to play out...it looks more impressive, which sounds silly, but people see your gear before they see, or hear your band. However, you can always add a 4x12 cab to a Mesa combo. Can even bypass the 2x12's and just use the 4x12 if you want.
I would start with a great sounding head, and a cheap cab, which can be had for around the budget line.
I picked up a used Mesa Dual Rec 3 channel head for $1000 on Ebay. (I already have one, but decided to try them in stereo

). I had a Crate 4x12 sitting around that I had picked up on Craigs list for $100. Was going to give it to my Daughter, who insist on having a half stack in her bedroom as "decoration"

. I've heard many Crate cabs, but never a good one. Decided to try the new Boogie head through it just for shit's and giggles. I haven't unplugged it since. Sounds really good. I can't claim that it sounds near as good as a Mesa cab, but it does sound surprisingly good.
So, for just $100 more than your buddy's budget, I got a seriously respectable half stack. Might not fit your friends taste, but the point is....buy a quality amp that pleases the players ears, and don't settle for "not bad for the price". At the very least, compromise on the cabinet, but don't skimp on the head.