Ebay. Absolutely. I buy all my clothing and footwear for work online. It is WAY cheaper for the same items. You just have to be sure which stores are trustworthy. Many ebay stores have thigh high boots, with a large variety of clours and sizes. Same ones I saw on that site link.
Hope this helps!
The main drawback is if you are in a rush to get them, although many online retailers are willing to ship extra fast for a higher price, and you still end up paying less overall than in Toronto shops, in my experience.