If you want to buy a SCJP voucher cheaply, instead of buy through online and pay in US$ , Just call to an pro-metric center in your city and buy the voucher in indian rupees, if you buy like this it may cost around 4500 Rupess (100 US$) only. You can find phone number of the pro-metric center in www.indiayellowpagesonline.com. In the same city SCJP vouchers are selling in different prices and can avail different percentage of discounts. So Compare and buy.
For Chennai NIIT is the authorized pro-metric center.