If you REALLY want a solid kb... Well, I know you want mx brown, but... There are some IBM Model F on sale in classifieds right now. Full metal case, sturdy, VERY good typing experience. But, of course, those KB are big and bucling spring could be just not your thing.
Thanks for the suggestion, but unfortunately the IBM Model M fails multiple requirements of mine: It must be a brown switch, it must have red backlighting, and it is not TKL. Plus, I also do not dig the aesthetics of it at all. It's a keyboard that would be cool for me to collect, but not for me to use as a daily driver.
Not model M. Model F. NKRO and full metal case. But, of course, it's not TKL and definitely not silent, so, although I own one of Model F, for working at night I got myself board with Matias Silent switches and AEKII.
But, as I said, If it not your thing, it just isn't 
But I still leave this link to classifieds. Maybe you'll want to add it to your collection.
https://geekhack.org/index.php?topic=68493.0
Thanks, but I want to make sure I perfect my primary keyboard before I ever think about getting another.
Orion 2 is TKL and very solid. KMACis always good
I'm not sure about the incline on the Orion though. I want a flat keyboard.
You could save yourself a bunch of money and get a Poker 3 when they're released. The cases are seriously solid and a small board actually IMPROVES the typing experience by being inherently stiffer than a larger board with the same technology / materials used. The case does have a little slant built-in, though.
OR get a Poker II without LED's and a Tex case and install red LED's yourself. <=cheapest option.
GON's boards are awesome and don't have any slant to them if you don't add the feet, but they're not as heavy as some of the metal case boards, although they're very "solid" in every way.
Ohhh, you're saying a smaller keyboard feels more solid? That's interesting. The Poker 3 looks like it will be out in a bit, not too far off.
With that kind of budget I'd look in Korean boards. KMACs, GON, and winkeyless are going to be a little easier to find and on the cheaper end of the spectrum.
I don't think Gon or Winkeyless does metal casing though. The Gon style is eye catching but right now I'm searching for something like the Kmac. (More on that and link at bottom of post.)
Nobody has mentioned GON yet.
Gons have been mentioned multiple times, including in the OP.
Some dude made a list:
http://cpkey.com/keyboards/
You can check those out.
Btw the infinity keyboard is going on in massdrop, definitely checkout that one too. With your budget you can easily hire some one to put it together for you.
Another option could be Tex Yoda. A poker + aluminum case is a good choice too.
Infinity looks cool but it's not really my thing.
Don't like the bottom 3 keys on the Yoda.
I've seen the list but haven't thoroughly checked it out yet. Will do it soon.
type now solid
I only see one thread linking to one ebay link for a keyboard which has sold. Not digging the orange... Prefer to grab a smooth-looking Kmac instead.
You could probably murder someone with a Ducky Year of the Horse if you don't want to wait for a Korean custom. It's a 60%, but it has red(and blue) LEDs, comes in brown, has a heavy-as-hell metal case, and felt pretty solid on the one I tried typing on at a meetup.
That's good to know! I'm not sure about the aesthetics of the YOTH though.

Hmmmmmmmmmmmmmm...
Unfortunately the keyboard community is too small to host large keyboard-testing-meetups.

i am currently putting together a kmac2, and i have to say that it could probably survive a nuclear holocaust. its litterally 5lbs of solid aluminum. the pcb is suspended on a plate. its the most solid keyboard i layed my hands on.
...
...
Dude... The things I'd do to that keyboard... Would probably get me banned if I say it on Geekhack.
http://www.overclock.net/t/1236288/kmac-keyboard-mania-attic-craft/0_100When I pull off all the switches I want to see that ^. Aluminum, metal everything.
That's the way it was meant to be meng.
...So uh, how does one procure a Kmac, because I feel like at this point I don't pick Kmac, Kmac picks me.
Hell, for that, if I can get it done and sent to me... with a few tweaks... I'd pay $600. Maybe more. Dunno.