An electric kettle uses between 1,000 to 1,800 watts of electricity.
That is a lot of electricity but the kettle is usually not on for very long and every time you boil a kettle of water or tea you're likely using maybe 1/2 a penny for each time you boil that kettle.
The electric kettle is only on for a short period of time and not hours like an electric space heater is.
So while an electric space heater uses 1,500 watts of electricity it costs more to keep the electric heater going because it's on longer than an electric kettle.
So actually it's pretty cheap to boil a kettle of water to make tea or anything else.
The electric kettle uses a lot of electricity but it's not really that costly.