1.OH GOD.. ARE YOU GOING TO USE SAME CAR FOR 20 YEARS.
2. Do you think you can get 18Kmpl from Vios ???? My ex boss has one and it does around 12 - 14 kmpl on average. Which means after in reality you will not save 6 laks after 20 years.
3. Waiting 20 years to cover the cost you spend over N16 (mind you that its not 6 laks profit after 20 years, but your cost will equal)
4. If you put that extra 6 laks on a fixed deposit for 20 years how much real profit you can earn at 10% average interest. After 20 years you will have minimum of Rs.3,669,545 in your account. Which gives you 3,069,545 or 3 Million real cash So you can spend your retirement peacefully. (some finance guy can help with exact interest amount here.. this is just average)
So the point if you take you desicion based on the calculations and assumptions you have done here.. it will be totaly lost interms of your so called profil (cost saving in reality).
How ever this does not mean N16 is better or Vios is better.. it is different matter to be discussed after all. However its just stupid to calculate expected cost saving over 20 years of time and take your desicion when buying a Car.