One thing you must consider, seeing that your budget is limited, is the running cost. Sure Passo and Vitz are better quality built cars and have more options than local (cultus) but you will have to keep them on petrol.
I do not need to state that even after the increase in prices, CNG costs almost half the price of petrol for similar mileage. So do consider your daily driving needs (in terms of mileage) before making your decision.
Also, if you go to remote locations/small cities, cultus will have better availability of parts and mechanics that both Vitz and Passo wont. Do keep that in mind too.
So if the above two points are of concern to you, go for Cultus...otherwise choose Vitz/Passo according to your liking.