Counting multiple instances of same name and calculating charges that exceeding 5 postings

I have names that appear in column B that may appear once or 30 to 40 times. Each of those names has a charge assoiated with it (column C). A contract was negotiated that states the charges will remain consistent up to five charges, and after that the customer (column B) will only get charged $5.00 per entry.

I need to count how many times the customer appears in column B, calculate how much they were charged, then figure out how much they were overcharged.