You about have to go Phenom to meet that price and the majority of the Phenom IIs are still slower than the Q6600. If the goal is medium settings you’d do fine with an Nvidia 7600 
Also, did I read that right? Did AMD pull an Nvidia and recycle older cards into the new family 
Here’s my shot. Little more but it’s also more powerful.
Thermaltake M9 VI1000BWS Black SECC Steel ATX Mid Tower Computer Case – Retail
Item #: N82E16811133058
$59.88 – $10 MIR
Thermaltake Purepower W0100RU 500W ATX 12V 2.0 Power Supply – Retail
Item #: N82E16817153052
$54.99 – $22 MIR
ASUS P5QL PRO LGA 775 Intel P43 ATX Intel Motherboard – Retail
Item #: N82E16813131329
$86.99
Intel Core2 Quad Q9400 2.66GHz LGA 775 95W Quad-Core Processor Model BX80580Q9400 – Retail
Item #: N82E16819115131
$189.99
CORSAIR XMS2 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Desktop Memory Model TWIN2X4096-6400C5C – Retail
Item #: N82E16820145241
$54.99 – $20 MIR
Western Digital Caviar Blue WD3200AAKS 320GB 7200 RPM SATA 3.0Gb/s 3.5″ Internal Hard Drive – OEM
Item #: N82E16822136074
$49.99
XFX PVT96OZDFU GeForce 9600 GSO 1GB 128-bit GDDR2 PCI Express 2.0 x16 HDCP Ready SLI Supported Video Card – Retail
Item #: N82E16814150340
$79.99 – $20 MIR
FREE – Call of Duty World at War
Use existing 16x DVDRW drive
Cost: $576.82
MIR: $72
Final Cost: $504.82