I have just sold my Baleno 2003 model, 85 000 KM driven, total genuine at 585,0000. Prices of cars are insane right now.
600,000 is the right price, if the condition is really immaculate. Otherwise, you can get Baleno's at 525 to 550 level as well. And you have to make sure that the Baleno you are buying drives well at petrol, as it is a treat on petrol.
Also make sure that the care drives smoothly in 2nd gear while on CNG, as it does give a few problems on 2nd care.
But it is a well manufactured car, gives around 125 to 130 Km's per CNG tank in the city and around 165 on long route.