I have a '2005 Toyota Corolla. For maintence purposes I would like to change the Brake Pads but can't recall if I should do both at the same time or only the front brakes. Any ideas?

To answer the question NO. You have a frount wheel drive car. THis means that when you stop you have the engine wight and the trans waight to stop. Thus the frount breaks wear out far faster then the back.
So change the frount when it is needed and have the back ones checked at the same time.
But to answer no, you can just change the back or the frount only when needed.

How much can i expect to pay for changing brake pads?