I took a continuing education at U of T and had a decent experience at the bookstore. Obviously university bookstores are overpriced, but you're also paying for the convenience -- I was OK with paying a bit more since I was only taking one course, and I could walk in, grab the books, pay for them and leave. I didn't find the books on Amazon and was too lazy to go running around the city looking for them.
If you can find your books elsewhere, definitely do it. But if you're lazy or there isn't that much of a price difference, the U of T bookstore isn't awful. I also liked the novelty of having a cute pink U of T clipboard, so maybe I'm just as big of a sucker as the first-years.