What the man above say ^
Fully agreed. GeForce 8800 GT is a good choice. It has the same "power" of the 9800 GT, and the only difference is some small features that you maybe never use, but the price difference is amazing.
BTW, I suggest picking PC 2 and changing some things: 4gb ram instead of 2 and change the vid card from 8600GT to 8800GT.
Because if you put an 8800 GT on PC 3, price would jump to 2500R$, which I think that can be expensive for your limit, (which you said it was around 2000R$)