Cheapest way from Pearson International Airport to Toronto's Downtown Train Station?

A cab will cost you at least $50, a shuttle anywhere from $10-30. Just take the TTC (Toronto Transit Commission). Follow the signs for the buses, take the airport express to kipling station. At kipling, you will go east (it's the only direction from there). I recommend getting off at the St. George station and just walking up to the N/S platform. You will want to go South to Union Station (I assume you're take Via rail) and then just walk upstairs. If you get lost, just stop somebody and ask.

G'day Paulthelimey: The trip is do-able by local transit as others have pointed out. The cash fare is 3 dollars Canadian, so you would need the change. However, as someone who has taken a local bus in New York City to save a few bucks getting from the airport, if you have more than a bag or two, buses and a few transfers after a long trip can be awkward just to save money; in this case about seven dollars. The airport shuttle bus service will take you to the Royal York Hotel, right across the street from Union Station. It's a bargain really, comfortable and usually pretty fast - depending of course on traffic. At the hotel you can even go inside, go downstairs to the shopping area and walk underground across the street to Union Station... handy if it's pouring down rain. If you walk into Union Station at street level, watch out for the red caps who are hungry to make a few bucks. Breathe in both places if you can. The Royal York was once the tallest building in all of the British Commonwealth! (Have a look at how it's dwarfed now.) Union Stations grand hall is massive. If you have to wait around there for your trip to Windsor, there are all kinds of fast foods and newsstands etc. on the GO Train side of the station downstairs. p.s. I've done the trip a few times and I think Via is the best way to get to Windsor. Good luck.