How much does hydrogen gas cost per gallon?

Hydrogen is not a liquid. So measuring it in gallons is futile. Ask your science teacher about the ideal gas laws, and this will make more sense.

NASA pays more than $4.50 per kg of liquid hydrogen (It doesn't say how much more.) That was the price in 2003 LH2. Fuel Density: 0.071 g/cc. 1 gallon [US, liquid] = 3 785.411 784 cubic centimeter Doing the math liquid hydrogen costs NASA more than $1.21 per gallon. Of course they buy in bulk because the shuttle uses almost 400,000 gallons per flight.

hydrogen is sold by the pound typically. The liquid hydrogen truck delivers us 6,000 gallons every month. But the price is related back to its source and it sells at 5 times natural gas price delivered as a liquid and 4 times natural gas price if shipped via a local pipeline. So, we pay $20/mmbtu. gasoline is now selling for $12/mmbtu. Propane is $20/mmbtu. so an equivalent price per gallon of H2 20/12 * the price of gasoline (then add taxes) generally, it's 1.5 time the price of gasoline. Of course, that's at the bulk station, delivery would add more cost than gasoline because of the handling. I'd guess that if regular gasoline was sell for $2/gallon, H2 would be $4/gallon, if..if...if...

You can get hydrogen from ammonia through an ammonia cracker. Ammonia price is around 300 $ / tonne (0.3 $/kg) and you would get about 2 m3 of hydrogen per kg of ammonia(about 17°000-21000 Kj). So you would have the equivalent of 1/2 kg of gasoline for 0.3 $ of H2...