depends what version your after, do you mean sp1....
you be looking at anything from around £70 [5,012.27 rupees] up to £160 [11,455.54 rupees] for oem versions of home, proffesional and ultimate and a touch more if you want the 64bit version.
the operating system does now ship with sp1 but even still win update has it on there anyway.
if you shop around you might find them cheaper and remember youll need a 64 bit cpu if you want a 64 bit os.
I think you can download the sp2 for free from the offical windows site, that's how they've done it in the past anyways.
but dont forget only OS wont work out you need to have all the drivers for your hardwares