At 650,000 u have several options, I would not recommend Toyota VItz 2000 because it is too old,
U can get Japanese Alto in good condition in this range, parts wont be an issue its automatic, good fuel consumption but i dont think it will give good performance on cng.
2nd option is daihatsu Mira u can get a 2006-2008 model Mira in this price range in very good condition, if u go for a 2-door mira u can get an unregistered 2008 model in 6 lakhs.
Suzuki Cultus is another option for u but try to find one in good condition.
The list for other Japanese imported car goes on...
Mainly it depends on u what type of car u prefer.
If u want to install CNG then dont go for Japanese imported cars, althu they do give very good mileage on petrol....