Cost of propane vs natural gas. The cost comparison between propane and natural gas is much easier to determine because unlike electricity, natural gas and propane can be directly compared based on their individual BTU ratings. Let’s assume the cost for natural gas is $15.00 per 1,000 cubic feet. This means that $15.00 will purchase approximately 1.03 million BTU’s of energy. This would be equivalent to 11.26 gallons of propane. At $2.50 per gallon of propane, natural gas would be a more cost effective energy solution. Breaking it down even further, natural gas needs to be more than $28.00 per 1,000 cubic feet for propane to be a more cost effective energy solution (provided the cost for propane is $2.50 per gallon).