I'm in a 70+ years old house but have a new 20 SEER heat pump for ~1450 sq ft with an ecobee maintaining 75F during the day.
ComEd lets me see my costs by day (and hour) and when I zero in on Aug 23 (Hi 99F/Lo 77F) it cost $3.42. This is not imo, excessive when my average daily cost is about $1.05 for electricity on a "normal" day.