Aryan post if you're still interested, i'll try looking up some online indian stores for parts if you haven't bought anything yet cause it's quite possible the people at the market will just rip you off. If you stretch your budget a bit you could build a low end pc that'll last you a while.
edit: nvm did already
Processor: G2020 at 2.9GHz at
Flipkart Rs. 3550
Motherboard: Gigabyte GA-H61M-S1 Motherboard at
Flipkart Rs.3048
Memory: Transcend DDR3-1333 2GB at
Flipkart Rs. 1599 and Rs. 1599 (buy it twice)
Graphics Card: NVIDIA GTX 650 at
Flipkart Rs. 7400
PSU: Cooler Master Thunder 450W at
Flipkart Rs. 2786
Total: Rs. 19982
I couldn't find a decently priced case that falls in your budget so I really recommend you use your old one or find an old used one from somewhere. This build should be quite sufficient for playing the new stuff in glorious 1080p at a low preset with decent enough frames.
EDIT 2: Bear in mind you'll have to put everything together yourself. You can watch some online video tutorials of how to go about doing that or take it to a local pc store, don't let them charge you more than 1500 Rs