I have not worked out a cost per hour but the 'slow' setting is 86 deg
so it's not going to use much electricity. I have cooked an 8 Kg turkey , a 4 kg Whole Gammon and a 3 Kg Beef joint all at the same time. Each was in it's own roasting bag so no cross contamination. There would have been room for a large Christmas pud as well if I had wanted one.
You can of course just do one small tight lidded saucepan of food if you want.
Due to the long slow cooking time you can put frozen joints straight from the freezer into the cooker , it defrosts and then cooks all in one. I have even cooked large pork joints straight from frozen, tastes great , melts in your mouth and never a problem. Just make sure you cook long enough, I do 8 hours minimum overnight. You can't over cook on slow I have left joints in for 12 hours or more , as long as it is sealed so that it does not dry out. Roasting bags are ideal for this, you can get ones large enough for a big turkey. Another tip is cook the turkey upside down! That way the juices run into the breast meat and keep it moist and tender, try it , you will never cook a turkey the 'right way up' again , you can even get special upside down turkey roaster pans to hold it in the correct position .