i get my rear tires from used tyre mart.....WONT skimp on the front end, cos they stop n steer.
i got a pair of conti sports 225/45/17 with 80% tread for $80 ea
i cant afford new rears all thee time, my mech 2-way makes short work of them, and the guys there are heaps helpfull.. they let me choose the ones i want.