How much money did you spend on the rig as it is right now?
Exact price? Well then, it would a take long time to calculate and wouldn't be precise either, but around 2800-2900 EUR (prices are inflated, totally dissimilar in Estonia).
I included an old PC that I had before, most of which I sold and built a new one, which I have already upgraded also.

How often do you update / buy a new rig?
If there is something that is getting old, or it's not powerful enough to run some kind of game on good performance (settings are lower than medium or picture is not good enough), then I start to think about new items, like GPU / CPU / RAM. But I try to keep going with the components that I have as long as possible.

What components are used?

• Monitor: Samsung SyncMaster 2493HM 24"
• Case: ThermalTake Aguila (the inside is painted black)
• Motherboard: P5K
• CPU: Intel Core 2 Duo e6750 @ 3.2GHz or 3.6GHz
• CPU cooler: Stock Intel cooler which is for some reason very good
• GPU: ATI Radeon Gigabyte 4870x2, overclocked with Diamond BIOS to 840/980
• RAM: OCZ Reaper HPC Edition DDR II 2x2Gb 800MHz 4-4-4-10 or 1066MHz 5-5-5-12
• PSU: ThermalTake ToughPower 700W W0106 with cable management
• HDD1: WD Caviar WD3200KS 320GB 7200rpm 16MB SATA 3Gb/s
• HDD2: WD Caviar WD7500KS 750GB 7200rpm 16MB SATA 3Gb/s
• HDD3: WD Caviar WD10EACS 1TB 7200rpm 16MB SATA 3Gb/s - Green Power 
• DVD/RW: Samsung SH-S183L
• Sound Card: Creative Labs Sound Blaster Audigy SE OEM
• Loudspeakers: Logitech 5.1  X-530
• Microphone: Genius Microphone MIC-01A Black
• Keyboard: Defender KM-4210
• Mouse: Logitech Mouse M-UV96 Black (like it more then any gaming mouse)
• Mousepad: Steelseries QCK Heavy
• Lighting: 2xGreen Neon & 2xUV Neon
• Scythe 'KamaMeter' with 4 Fan controllers, 4 temperature sensors, etc...
• Operation System: Windows Vista Ultimate SP1 and Windows XP Professional SP2 for overclocking and testing (3dMark06, Super Pi, etc.)