How do i use the adverb?
Can i say “those discs were not yours to begin with. So, you should not be complaining about their quality.”? Or, do i need to use “to begon with” at the beginning of a sentence?
Also, is there any difference between “different costs between cars A and B” and “different cost for cars A and B”?
Yes, I believe that “to begin with” should be at the end of a sentence, just like in your example.
The position of this phrase depends on the emphasis you want to put on it. If you use it at the start of the sentence, you are making the point more strongly.
I would change the first sentence to: The difference in cost between cars A and B.