silly question(I'm a noob):I don't how to overclock
and how much does a sandy bridge cpu cost?
That depends on your system:
Motherbord:H67 based would cost around Rs5000-6000k
P67/Z68 based starting from Rs10k and above.
CPU:if you chose H67 bsed chipset,then you should go for i5 2400(NO OVERCLOCKING),price around RS 9k
if you choose P67/Z68 ,go for i5 2500K/i7 2600k.(EXTREME OCing),Price around Rs10K.