In your budget of Rs 5 to 6 lakh, there is no brand-new four-cylinder bike available today. Therefore, your only option is to look at the used market. Bikes that should be available in your price range are the Honda CBR650F, Kawasaki Z800 / Z900, and Triumph Street Triple 675. Do bear in mind that you're looking at machines that are nearing 10 years of age - possibly even more - and buying a machine with a documented service history would be advisable, even if it means paying a little bit more, as replacing mechanical or electrical components on these bikes will cost you a pretty penny. Also, none of these bikes are E20 fuel compliant, which is another factor to consider.