The service interval for i10 is 10000kms or 6 months which ever is earlier. ( service adviser once told me that if sometime I cover say 5k-6k kms I can get the service done in the next month. )
I have owned i10 and santro for around 4.5 years. Normal service was around 2500rupees. Oil, oil filter, air filter + periodic maintenace.
For the past 2 years haven't calculated i10's mileagr because my dad drives it but he says car gives around 10kmpl in city traffic in summers. Just had a tankful yesterday and I reset the meter, so I will tell you the latest fe if I get a chance.
About other service parts. If some part needs to be changed obviously the bill would come very high.
I changed i10's clutch and believe me local mechanic said to get it done from service center because the difference was just 500rupees ( 5000 from outside, 5500 from company) Hyundai Trio: Santro, i10 and Verna !
But yeah I prefer to get my car serviced from outside. The bill comes exactly half at 1200-1400 rupees.
But after 15-20 k go to service center for thorough checkup.