Compare prices for airfares. There are huge differences. The following websites have good prices for international and student travel:
Check STA travel. They have student discounts, and you can usually change your return flight with a minimal fee. They also allow you to reserve your flight for a small fee and pay later. Look for the Book Now, Pay Later!
kayak.com - This website searches all the other on-line travel sites.
travelocity.com - A reliable resource, but it is not always the cheapest.
Always check the airlines website also because they often have discounted fairs.