Total (with tax): $1046.30
MIR value: $100.00
The only reason why I picked the 7870 was because it seemed like such a good deal at it's current price, but I am thinking now that it may be overkill for his resolution. Some of the games he would like to play include Arma 2, Skyrim (with graphics mods), Starcraft 2, possibly BF3, and the Total War series of games. At 1440x900 though, would I even need the 7870 or could I go lower than that without compromising the longevity of the system?
Otherwise, my goal is to try and reduce the cost of this build as much as possible. I could forgo the hard drive altogether as he already has a 120 gb drive, but if costs could be reduced elsewhere it would be preferred.
7850 is more than enough to max out any game at the moment on 1080p, even Max Payne 3. The best GPU for you sounds like the GTX 660, if it sells around the $200 mark and you can wait for one more week.
And you will need that 1 TB hard drive, modern games are getting bigger and bigger and that 120 gb will be used up really quickly.
If your brother does not want to overclock, you can also drop to a i5 3450 and a H77 motherboard.
And a 500w PSU will be good enough for this setup, I recommend the Antec HGC 520w.
^Sorry, but that's just wrong. It takes a 670 to max games like Crysis 2 and BF3 on 1080p, with maxing defined as 60fps on maximum settings.
You should get the best possible graphics card within your budget. If that's a 7870, great. A decent 650W PSU will be enough for two later.