What is causing my electric bill to be so high?

My husband and I are wanting to buy the house we are in now. We have a pretty sweet setup. His grandparents own the house and pay the electric bill and we pay the mortgage. And believe me we have the cheaper of the two. We have insulated everything we can think of from windows to doors to attic, basement, and garage. Our electric bill on average in the winter time runs around $900/monthly and like right now when we are only using a fan in the window, around $400. We do have base board heaters and i know that's part of the problem. But what could be causing the bill to be so high when we are using just normal lights and a fan? Is this fixable? We don't want to buy something that is going to be that crazy high of a bill. Any suggestions?

Read more: What is causing my electric bill to be so high?