。
I had to pay an additional five dollars.
Literal
I [topic-は] additionally 5 dollars pay must-not-be-without.
~なければならない is the standard 'must, have to' construction — literally 'if not, it won't do,' a double-negative that resolves as obligation. さらに ('additionally, further') layers on top of an implied previous payment. Dollars signals the sentence is set in a context involving USD.