Well hello,
With 45k as a salary and still teen and close to me age, dont waste the salary when you are just starting to save money. Also if you are planning to take a lease/loan, trust me it will bite you in the sweet spot if you dont manage carefully. Save a bit more, but with the Lankan vehicle market is bloated with the Japanese mindset and unrealistic prices for second hand cars, you are better off buying a new car (ex: viva elite, axia, i10, picanto) which is new.
Also dont buy a old rust bucket if you dont have time to attend to garages and repairs and so on. Im thinking that you will be doing some professional qualification studies of some sort. If so, never buy a rust bucket. IE: You can buy a Fiat 131, YOM 1977, it does good on fuel and all. And costs -=200k. But with the age of the car, rust is a issue. This is just an example.