Sorry, I should have been a bit more clear. Used in stores only saves about $5.
Online is an entirely other matter.
I tend not to even look online simply because whatever I'd save in original price just gets jacked up by shipping costs and import charges. I mean if the game is $30 US plus $10 for shipping and then another $10 for import fees the game already costs $50 US. Which I then have to convert to Canadian dollars, which raises the price by basically 20%. So a $30 game ends up becoming $60 afterall. And for all that effort, it's just easier to either pay for the used copy (from a store like gamestop) for $5 less or buy new for ~$15 more (over the $60 price mentioned above).
Perhaps in the US buying online saves you money, but in other countries? Not so much.