I did my first change at 1000km using KIA's semi synthetic and then again at 8000km and went full synthetic. The KIA dealer here uses Quakerstate full synthetic and it costs me $75 for a full Schedule 1 maintenance with synthetic.
I use my car mostly for work and will do my 8000kms in about 3 months. I am planning to drive it for work for 5 years and then pass it to my wife for another 5 years (while I drive my new car!) With that in mind, I bought an additional 2 years and 60,000km warranty to total 7 year 160,000km and switched to synthetic in an effort to make sure it lasts the full 10 years. (the 10 year 100,000 mile/160,000 km warranty is only in the US, Canadian warranties are for 5 years and 60,000 miles/100,000 kms)
To some of you, especially in the US, $75 for an oil change may seem high, but where I live, that's even cheaper than the Penzoil 10 minute oil change place if you want full synthetic.
Also don't forget, because I use my car mostly for business, I'm paid a car allowance (covers all but $22 a month in payments), I'm mileage to cover maintenance (that account is still growing every month) and everything I spend on my car is a write off!