@browncoat - It was probably costing you way more than it had to in electricity bills as well. When we moved into our new home the first thing we did was look at the insulation for the hot water pipes, since pipe insulation can bring down the bills as well. And it's pretty easy in that case, since all you have to do is wrap some insulation around it.
I wouldn't try to do a DIY oven insulation job though, unless you know what to do. It might be better, in that kind of situation where the landlord isn't helping, to just get a toaster oven or something like that.