Everyone is aware that sustainable H2 has to be brought down in price to be comparable to gas/mile. DoE's target is $4/kg, untaxed, which would be below the per mile cost of gas for most vehicles in most markets. Whether they can get there remains to be seen, but that's why they and others are spending R&D money to reduce the cost/increase the efficiency of electrolysis, and are also exploring other avenues. See https://www.greencarcongress.com/hydrogen_production/ for examples.
In the meantime, H2 from excess renewables is essentially free, not counting the cost of the electrolyzer etc.