If you like Pirellis, try George at Turn2.ca. Or if you're out west a bit, call up Richard at RCC. Zdeno's has decent Bridgestone pricing (but again, a bit west of the GTA, 519 area).
Not much of a major retailer, but I was at Rosey Toes the other day and he told me that he's now selling new sets of Metzelers for $300, tax included and mounting included. That's roughly what I pay for race takeoffs once I factor in the tire mounting.
I don't know what model of Metzeler he's selling, but you might want to give him a call.
Georeg at Turn2 was doing Pirelli Diablos (front and rear) installed for something liek $300 plus tax. Corsas for not much more.
Ask Richard/RCC, see what he has for Pirelli pricing.
Pilot Power seem cheap, got a deal from somone I know there for one of my bikes for a Pilot Power for $180 for a rear. So front and rear should be around $300 too.