Near impossible to buy that kind of PC in that budget but here goes. I hope that you have a hard drive and casing with you already.
Motherboard: LGA1155 used = 3000 RS.
Processor: G2020 new = 6300 RS. (processor not too good for GTA IV cuz its Dual Core, GTA IV recommends Quad, but its outta budget. Still best for this budget.).
RAM: 4 GB DDR3 = 3000 RS
Power Supply: Good China 500W = 1000 RS.
Fans + Wires = 300 RS.
GPU = 6750 used = 7000 RS.
Total = 20500.
With this setup, you will be able to run Crysis 2 at a mixture of medium-high settings and similar settings for GTA IV at 720p with good framerate (30-35). However if you want to buy a hard drive and a casing as well, then I don't think you could accommodate that within this budget. Because you will get the hard-drive for around 3500 RS, and a casing for 1000 RS.
I suggest you increase your budget by approx 5000 RS and get a better graphics card like 7770 used.