What is cheaper to run, portable electric heater (assuming standard electricity charges) or indoor portable gas heater?
Well, I don't know about cheaper, but if you use a portable gas heater indoors, you must be sure that it is vented. Otherwise you will end up like my neighbors of 20 years ago. They hooked up a portable gas heater in their bedroom and never woke up the next morning. Their friends found them both dead in their bed.
gas is cheaper
indoor portable gas heaters can not be used in many situations depending on the state and such. Same with the old Kerosene heaters which are also an alternative.
gas is cheaper
The safer of the two is the electric. You never run a gas heater indoors. Poisonous gases kill you dead.
Depends ion the relative price of electricity and gas where you are. By "portable gas heater" I assume a heater not connected to mains gas ("natural gas") and using gas from a cylinder in the heater. Look for the output of the heater in kilowatts and compare it with your electrical heaters - typically around 1 kilowatt to 2 kilowatts. Then see how much fuel each uses per hour.
The cheapest heat available is an electric blanket. Most use only 100 to 200 watts. Put it on your bed, turn it on, and crawl under it.
Can't tell without knowing the prices of electricity and gas where you are--what kind of gas, anyway? What is a 'standard' electricity charge? Within North America, it can be from 7 cents per kWh to 31 cents. And we don't even know if you're in north America.
gas heaters are NOT for indoors! EVER! they create poisonous fumes and are safe ONLY outdoors
Electric heat is almost always the MOST expensive option.