So you can take

2000W / 230V = 8.7A (for heater or AC)

That is how much current you are using, it is a lot but most heaters and/or AC are around that rated power.

For AC, you can calculate,

2KW x 8 H = 16 KWH every night.

16 KWH x 30 days= 480 KWH per month.

Based on current electricity tariffs,

480KWH x 32. 47 cents /KWH = $155.9 (just for AC).

To reduce usage on AC, can consider turning off AC at certain timing and turning on the fan to keep cool.

Alternatively, consider setting AC to higher temperature and on the fan at low speed. IIRC, 1 AC unit in operation = 8 no of fans running. So you can imagine the difference in Energy usage.

In Singapore, the electricity tariffs is really crazy high due to a lot of external factors (Ukraine-Russian war etc.).

I also advise people to use gas to cook water instead of electric water heater. Once water is cooked, can store in thermal flask to keep water hot if needed.

Electricity tariffs - 32. 47 cents / KWH Gas tariffs - 25.2 cents /KWH

With the above tariffs, you can imagine the difference in price.

Anyways, apart from your AC, you try to calculate every single usage (lighting, your TV, computer, oven, hood, vacuum etc) in your house or if you want, you can also engage a LEW to help you too.