Translation:The hotels next to the sea are expensive.
My Hungarian girlfriend said that she would rather say: A tenger melletti szállodák drágák.
The accusative is only used for a direct object. There is no object of any kind in this sentence.
neben dem Meer -- I see no object at all but rather a prepositional phrase with the dative.
In Hungarian, I think nearly all postpositions take the nominative case.