I don't believe you'll find a 2017 model Santro in your budget. If it's an older model Santro then it would be a good idea to first check where you can get its genuine parts and their cost.
Santro is no doubt better than Mehran or Alto but you'll find mostly many years used models so finding a clean car will be difficult. If you buy a car with a lot of chaira chaari such as cheap parts, not matching parts, improper electrical system mods such as HIDs, etc. then fixing those issues will take up a lot of your time and money.
Genuine spare parts will also be more expensive than Suzuki since Santro is no longer built here so its parts are imported and incur hefty duties along with high profit margins.