Last year we all pitched in with donations and I built a squaddie a system with limited funds as his old computer was.. well I'm surprised it even loaded AH! It was so old and so slow that his vox would make the game cut out and he was struggling to see 10fps with all options OFF and that limited him to goon running (barely).
Anyway, working with a strict budget of $500 I was able to build him something that runs AH quite nicely. With all graphics options on except shadows he see 55-60fps all of the time at 1920X1080 resolution.
It really was nothing special.. an AM3 motherboard, 4GB DDR3 ram, 1TB Hard drive, ATI Regor processor (2.7GHZ if I remember correctly), ATI 5770 video card, 650 Watt Seasonic power supply, cheap computer case, cheap DVD-rom. It actually turned out to be much faster than I was thinking!
We also had a squaddie donate a monitor and another donated a copy of XP Home for him so that $500 was for the computer itself only, so yeah your $800 can go VERY FAR if aces high is your primary game.