Beggars can't be choosers. The whole idea is to replace gasoline and diesel. The added expense is academic since the expense of climate change cannot be willy nilly excluded. The ammonia is supposed to be produced using windmill and solar panel power plants thereby resolving the intermittency and timing problem with these alternative power sources. Their biggest drawback aside from short term deployment costs. Using a liquid fuel storage approach is self-evident. But using H2 instead of NH3 to do this is not smart. Handling H2 is not going to be any cheaper than handling NH3.
But we are in another idiotic race for time where enough propaganda from H2 fuel boosters can commit us to some sub-optimal solution. NH3 has substantially less drawbacks compared to H2.