My first build was around $1500 for DFI LanParty NF4 Ultra motherboard (I used the pencil hack to enable SLI), Athlon64 X2 3200+ CPU, 1GB OCZ DDR RAM, WD 74GB Raptor, MSI 6600GT GPU, NEC DVD-RW drive, Thermaltake Tsunami Dream mid-tower, OCZ 500w modular PSU, Saitek Gamer's backlit keyboard, Hyundai 19" LCD monitor, Logitech MX1000 cordless laser mouse, Logitech 5.1 speakers, and a Windows XP OEM license. I overspent on motherboard, memory, and hard drive, and underspent on CPU and especially GPU.
Over the years I spent probably another $500 to upgrade the CPU to a 4000+, double the RAM, replace the GPU with an 8800GT, and add a DVD-ROM.
When I built a new system, I spent about $800 on an Asus P5Q Pro LGS775 motherboard, Core 2 Duo E8500, 2 GB OCZ Fatal1ty edition RAM, 600x OCZ PSU, WD 640GB HDD, and a Windows Vista license. I kept the case, Raptor, and peripherals, and put all the rest of the old stuff (along with a $20 fanless GPU and a 640GB HDD) in a new $50 case for my wife to replace her Dell desktop.
Since then I have gone through a GTX260 GPU ($180) and a 480GTX ($220), upgraded to a 24" Asus monitor ($180), replaced the PSU ($80), added a Noctua 120mm case fan to the side window ($15), upgraded to Windows 7 ($80) replaced the mouse twice (Logitech MX1100 for about $80, and then a G700s for $50), and I picked up an OCZ Alchemy Elixir keyboard for a dollar after MIR.
All told, with the things I have listed here and the things I missed, I've probably spent about four grand on hardware and OSs building and expanding since 2004, and I have two functioning computers out if it plus assorted spare parts and things such as old GPUs installed in other family PCs. I'd love to spend another $400 on an LGA1150 mobo, Core i5 4690K, and 8GB DDR3 RAM, but financial priorities and responsibilities have changed over the years, so I'll be rockin this Core 2 Duo for as long as it lasts!