If you already have a computer and just want to upgrade it to a gaming rig, all you need is just a new unit or the so-called "cpu only" by many. Anyways, take a look at this gaming rig for less than 15,000 pesos.
Processor: AMD Athlon 64 X2 240 2.8Ghz AM3 - 2,950.00
Memory: Kingston 2GB PC5300 DDR2 667 - 2,150.00
Hard Drive: Seagate Barracuda 320GB 7200rpm SATA -2,200.00
Video Card: PowerColor HD4650 512MB DDR2 128Bit DVI - 2,480.00
Motherboard: ECS G13M Intel G31 PCIE/A/V/L/ -2,100.00
DVD Writer: Liteon DVDRW IHAS-324 24X Sata - 1,275.00
Casing: Gleam GM03A ATX 500W - 1,180.00
Keyboard: A4tech Comfort Key KR-85 -285.00
Mouse: A4tech OP-620 PS2 Optical - 220.00
The prices for the above equipments were based on pcgilmore in Gilmore Quezon City Philippines. So it will vary defending on the computer shop where you will buy. It is ideal to look for different computer shop in Gilmore Center and ask for their discounted or packaged price.
You may also ask for upgrades where you can have a higher processor, memory or video card for additional fees. But somehow, that will give you idea for you budget gaming pc for this christmas. Enjoy your bonus! :)