What's the cheapest place to buy airline tickets to travel in Canada?

I want to go from London Ontario/Toronto Ontario/Hamilton Ontario to somewhere in Prince Edward Island (probably Charlottetown) for four weeks to visit family. I heard from someone it should cost only $300 to get there and back, but I can't find anywhere that offers that price - the cheapest I could find was over 700 bucks. Any help?

Check out kayak.com that performs a meta-search for you of all airlines.

I would definately advise you to book for flights with either Expedia.com http://expedia.com/ or Travelocity http://travelocity.com/. They have the cheapest fares around - and the service is user friendly, and you have many choices of flights, especially if the route is popular.
Bon Voyage!

There are 4 airlines flying from Toronto area and PEI -- Jazz (Air Canada), Northwest (if you could go from Detroit), Westjet, and Sunwing. Try booking direct from their websites.

Westjet looks cheapest currently, with some options about $434 CDN roundtrip, but I didn't check Sunwing which might be cheapest.