Ya Alan, Getting the return ticket at the end of the contract is normal. It is actually cheaper if the school buys a return airfare.

If you are concerned about getting your severance pay (1 month's salary, ususlly 2 million) at the end of contract (called taechicum here) then ask that it be paid in monthly increments (as done in most of the world). In other words, your salary would not be 12 x 2 million/month = 24 mllion/year but 26 million/year. Understand? If more teachers asked for this there would be less fighting and disappointment at the end of contract. Don't accept Saturday or Sunday teaching unless it is for a lot more money. It will burn you out. Teaching load is heavy in Korea, usually 120 hrs/week.
Stay healthy.