If you insist on buying new than you can also consider Chevrolet Joy. A brand new, CNG fitted, EFI, powerpacked car for around 5.5L.
Santro and Cultus are both extremely over-priced cars. But, I would chose Santro if I had to chose between these two. Santro lacks rear leg room and the seats aren't that comfortable. Other than that, it is a good car. Cultus is a car from the past. I just can't spend more than 6L on a 1989's model.