ADSL (Asymmetric Digital Subscriber Line) is the technology used in Toronto Free-Net's residential high speed service. We often abbreviate that to just "DSL".
All ADSL modems, that were manufactured in the last decade or so, work with TFN's service. The price of the modem mostly depends on the extra features it supports, such as wireless capability and the number of wired computers that can be simultaneously connected.
There are about 15 computer stores around the intersection of Spadina & College. It's a good area to shop around (though computer stores in other parts of town have good prices too). All four streets flowing into that intersection have computer stores, all within four blocks of the intersection. Most of the stores are along College, west of Spadina.
Following is a random list of brands that offer DSL modems. Use this to search the web for second-hand DSL modems.