All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.
A Muslim who is pleased with Allah as his Lord; Islam as his religion; and Muhammad as his Prophet should have mental, instinctive, and material evidence that gives him certainty about the truthfulness of the religion of Islam, that the Quran is the Word of Allah, and that the sayings of the Prophet are true.
It is inconceivable that such a believer would have doubts about the religion of Islam, his Messenger, and the Book that was revealed to his Messenger just because he does not understand the wisdom behind one of the secondary Shariah rulings, especially if this secondary ruling was deduced through the efforts of the scholars and is not stated in the Quran or in the ahaadeeth of the Prophet nor was agreed upon by the consensus of the scholars of Islam.
If the matter with you has reached the extent which you described yourself with in the question, then you do not need to know the wisdom behind the difference of the Diyah (blood money) of a non-Muslim from the People of the Book and a non-Muslim from other religions; rather, you are in dire need of learning what increases your belief in Allah and strengthens your faith about the truthfulness of the religion of Islam and the fact that the Prophet was infallible and that what he came with was all true. This knowledge can be gained in books that deal with the atheists and those who are skeptic about Islam. We ask Allah to guide us and you to His righteous Path, as we ask Him to spare you from (the devil's) whispers.
As regards this issue which confused you and almost spoiled your prayers; then you should know that it is one of the issues of Ijtihaad (personal reasoning) of the scholars and their method in analogy, explaining the rulings, and consideration of the purposes of the Shariah; it is for these reasons that they differed in opinion.
Some of them are of the view that the Diyah of all non-Muslims is the same, meaning half the Diyah of a Muslim, whether they are from the People of the Book or from others who are living under the Muslim rule. Some other scholars are of the view that the Diyah of non-Muslims is the same as that of Muslims, and some of them are of the view that the Diyah of the non-Muslims other than the People of the Book is different from that of the People of the Book because their religion is inferior to the religion of the People of the Book.
Therefore, investigating this matter does not benefit you in anything, and knowing the truth about it is not a priority for you.
Allah knows best.