Electric space heaters do cause high electric bills.
Electric heating with electric space heaters is the most expensive way to heat a home and use of just one electric space heater can cost you around $1.50 to $2.00 per day of run time depending on your KWH cost and how long you run the space heater.
A space heater consumes 1500 watts of electricity per hour which is a lot of electricity so your electric bill will go up when the electric space heater is in use.
It costs on average of 15 cents to 20 cents per hour of run time for an electric space heater depending on your electricity costs.
I once had to try to heat a house with 4 electric space heaters running constantly and my electric bill went up to $500.00 for that month.
My natural gas bill is only $150.00 per month and my house stays much warmer.