What should one do if they fear missing the school bus after praying Fajr in congregation: Should they pray alone, and would paying money for late transportation be considered a hardship?

May Allah reward your diligence. Know that congregational prayer in the mosque is not obligatory. So, if someone who fears missing the bus prays in congregation at home with some of his family, he would have fulfilled the obligation, and his responsibility would undoubtedly be discharged. And assuming he found no one to pray with, it appears that this is an excuse that permits him to forgo the congregational prayer and pray individually.