Oil shouldn’t cost above 8.5k rupees. That’s the best 0w20 oil available locally in official capacity ie Havoline ProDS.
Easily runs 8k to 10k km.
Genuine oil filter will also be not too heavy on the pocket if you buy from third party shops. Same for air filter but can also go with third party air filters doesn’t have to be oem.
Can you break down how you’re getting to 16k?