I baught my second hand 03 Corolla on Sep 2006, after the first oil change about two months ago, I went for a trip (around 600km) and upon checking the oil level I was shocked to see that it was empty (no signs of blue or white smoke, or oil leakge, or low oil indicator, or even high engine temperature). I added oil (about 2-3 liters) and started checking the level every other day. In the next 500kms the oil level wasn't reduced (I was driving inside the city, mostly below 80km/h). Then I went to another short trip in the highway (about 300km, below 120km/h) and the oil level was below the lower line (in the dipstick).
My question is what are my options and approximately how much are the expenses. I baught the car as a second hand from a Toyota Dealer.