3K? Wow. My rig, which is about 10 months old (I got it for Battlefield 3), consists of:
4GB DDR3 1666 RAM
Coolermaster HAF-12 case
Seagate Momentus XT 500GB hybrid hard drive
Asrock P67 Extreme mainboard
2x Radeon HD 6950, modded to 6970, in crossfire
Nvidia GeForce GT440 (for Physx only)
Microsoft Sidewinder X6 keyboard
Saitek R.A.T. 7 mouse
I paid about 2000USD for that rig back in the day, and it runs Battlefield, Metro 2033, Crysis 2 (with the DX11 high texture mods) and everything else I throw at it at the highest settings at 1920x1200. Most games run at 60fps; no game dips under 30fps apart from Mafia II where I do have to tone down the Physx to medium.
I recently upgraded the keyboard to a Thermaltake Cherry MX red keyboard and added a Corsair Force 3 240GB SSD and even then with the upgrades the rig still comes in at under USD2,300.
I'm guessing this rig should cost 2/3 to 1/2 what I paid today, and you can still run games at full-bore for the near future - at least, until Battlefield 4 comes out, heh.
I assembled it myself, although assembling a computer is very easy. I helped my brother in law to order and assemble his over the phone, and he lives halfway around the world. A quick youtube search and you should be able to find a nice guide to help your brother along the way. Just set aside about two hours for the first build - your brother might even learn something valuable along the way.
Having said all that, what games does he play / plan to play? If it's World of Warcraft, then anything over USD600 is overkill.