How much should I pay for a GTX 750 Ti?

To be a good deal: Is it adequate for your needs? Can you buy something as good or better for the same price or less?

There is no established list of 'good deals'. One person may not want a 750 Ti no matter how low the price was, someone else might be willing to pay list price for a new one.
 
The cheapest pre-owned one I could find was $100AUD, and the cheapest new one was $135AUD, so I would say $60 is a very good deal. However, prices in Canada could be very different so just look around on popular websites. (AUD and CAD is almost the same)