Which option fits best: We were left without any money for the last part of our holiday because we had ____________ the cost of the train ticket to Norway.

The best fit for the sentence is the choice that indicates a failure to accurately assess the cost. "Underestimated" suggests that the costs associated with the train ticket to Norway were perceived as lower than they actually were, resulting in not having enough money for the holiday's final portion. This word correctly conveys the idea that there was a mistake in judgment regarding expenses.

Using "underestimated" aligns seamlessly with the context, as it explains the reason for being left without money. The other terms, while applicable in different contexts, do not convey the same meaning relevant to the financial shortfall outlined in the sentence. For instance, "overestimated" implies too high an expectation, which would not support the scenario of running out of funds. Similarly, "estimated" lacks the necessary connotation of a misjudgment regarding costs, and "misestimated" is less commonly used and not as precise in this context. Thus, "underestimated" is the most appropriate choice, effectively communicating the misunderstanding of the train ticket costs.