How much is my PC worth? Estimates please.

Basically, I just want to sell my old PC i've been using for a couple years, and I want to get an estimate on what it is worth or how much the parts are worth.

Dell Optiplex GX620 3.0GHz Tower Computer

Processor: Intel(R) Pentium(R) D CPU 3.00GHz (2CPU) ~3.0GHz

Motherboard: Dell HH807

Power Supply 375w

Memory: 4gb
Kingston PC2-4300 1GB DDR2 RAM (266MHz)
Kingston PC2-4300 1GB DDR2 RAM (266MHz)
Nanya PC2-5300 1GB DDR2 RAM (333MHz)
Nanya PC2-5300 1GB DDR2 RAM (333MHz)

GPU: NVIDIA Quadro FX 3700 512MB

Hard Drive: Hitachi Deskstar P7K500 (500GB, 7200 RPM, SATA)

Optical Disk: PHILIPS DVD+ -RW DVD8801 ATA Device

Case: Dell Optiplex GX620 Tower Computer

Monitor: Samsung SyncMaster P2770

Keyboard: Microsoft Sidewinder X6

Mouse: Logitech M215


If anyone can give some estimates that would be greatly appreciated.