For $1200-$1500, you can get two Dell-based systems. Or one Dell-based system, a good monitor, and CH Products joystick and pedals.
In my opinion, the only weakness of a Dell system is the power supply -- the rest of the components are fine. You can get a high-quality 400-500W ATX12V power supply from Newegg for $50-$75 (Antec, Corsair, Coolmax, Thermaltake, Seasonic -- take your pick).
Overall:
Dell Inspiron 660 is $500 (i5-3330, includes OS, 500 GB HD, 4 GB RAM, DVD+/-RW, 100/1000 Ethernet, sound, keyboard, mouse)
Thermaltake 500W ATX12V power supply is $50 (from Newegg)
Nvidia GTX 650 Ti (rated best for price range by Tom's Hardware) is $130 (from Newegg)
total = $680