How old is your house, and how large? There's no way a house built to today's standards should cost that much to keep cool in the summer (or conversely keep warm in the winter). My house (3,500 sq.ft.), built three years ago with low solar heat gain windows and properly insulated costs less than $100 for electricity in the summer with full a/c and my highest gas bill for heat (last January) was $87. It sounds like you either have a monster house or it's old enough that it's framed with 2x4's instead of 2x6's, has low quality windows, and/or isn't insulated to the same standard as today's houses. When I'm talking of standards, I'm referring of course to Canadian construction standards (seeing as you're from Edmonton), which are considerably higher than U.S. standards and several times more energy efficient.