This is the 3133rd most frequent Dutch word.
duurste
Most expensive.
Here, 'duurste' is the superlative form of 'duur' (expensive), describing the noun 'auto' as the most expensive compared to others.
Dit is de duurste auto die ik ooit heb gezien.
This is the most expensive car I have ever seen.
In this sentence, 'duurste' again serves as the superlative of 'duur', applied to the noun 'vakantie' describing it as the most expensive among a group of vacations.
Van alle vakanties die ik heb gedaan, was deze de duurste.
Of all the vacations I have taken, this one was the most expensive.
Here, 'duurste' describes the noun 'product', indicating the speaker is referring to the most expensive among various options.