A $400 bill at $0.50 per kwh is 800 kwh. Our electricity usage in the month of August was 787 kwh. I wired an energy meter into my circuit panel a month ago, so I can break that down:

• 210 kwh for EV charging. I don't drive a ton and can also charge at work sometimes. This is 27% of our total
• 130 kwh for AC. We live in SE MI, so it's not hot. We keep our AC set to 75 when it's on. These two combined are now 40% of our bill
• 62 kwh for my work desk (hybrid work) and deep freeze
• 61 kwh for our furnace blower motor. This one surprised me. We were leaving it on the low setting to equalize temperature. On the low speed it pulls 500 watts, or 12 kwh/day. It obviously pulls more power when the AC is on
• 61 kwh for our fridge
• 28 kwh for our washing machine and gas dryer
• now we're in odds and ends territory. 17 kwh for our instant Hot water (tea), 12 kwh for our sump pump and dehumidifier, 11 for our dishwasher, 8 for the TV (old fluorescent)/garage/ps5/modem/route, 7 for the microwave
• another 100 or so that doesn't have a clamp on the breaker

If you don't have an EV and you're really keeping your AC at 84 I strongly suspect you have a failing appliance. Unless you live in Phoenix and have a massive and very poorly insulated house or something.

During covid (I was doing remote work, so basically no EV charging), our old dishwasher finally stopped working with a dryer heater error code. When we replaced it our electric bill fell by a double digit percentage (I want to say 20%+) year over year.

As for things like insulation, going from 3" of 1969 insulation to a massive quantity of blown in helped our winter heating bill (gas) a lot more than our summer AC bill.

Good luck!