I can't say it like that. It depends on the difficulty. (The characters are not the only factor of the difficulty!)
Give me an example, what prefix you want and case-sensitive / case-insensitive.
Ok, lets take examples like:
1 - 6 letters after 1 - example: "1dodgra" - how much you will charge for that?
2 - 7 letters after 1 - example: "1dodgrad" - how much for that?
3 - 8 letters after 1 - example: "1korrupte" - how much?

Question - If i want change letters in this examples above - for example not "1dodgrad" but "1DodGrad" - do this will change system and price?
No need to mention "question" as a question mark is enough to make them understand its a question .