Due to new hardware, I suggest the following changes to the ultra low-end, low end, and mid-end computers:
CPU
Ultra Low End: Sempron 2800+, AM2, 50 dollars.
http://www.newegg.com/Product/Produc...82E16819104301
Low End: Athlon X2 3800+, AM2, 150 dollars. (Newegg is down at the moment)
Midrange: E6300, Conroe, 200 dollars (Newegg is down)
High-end: E6600, Conroe, I forgot the price (See above)
Mobo:
AMD:
Basic: The cheapest at the moment. Any would do.
Overclockers: The DFI infinity, 100 dollars.