Learn Finnish: Meillä ei ole varaa tehdä pitkää ulkomaanmatkaa tänä vuonna. - We cannot afford to take a long trip abroad this year.

It literally translates to "at us is not the resources". It uses the possessive structure: the adessive subject (meillä) + the verb olla (ei ole) + the partitive of vara (varaa, meaning means or funds). To say what you can't afford to do, you just add a basic dictionary-form verb (first infinitive) right after it, like tehdä.

Why are the words pitkää ulkomaanmatkaa in the partitive case instead of the accusative?

Because the main clause is negative (ei ole). Even though the object belongs to the infinitive verb tehdä, the negative reality of the whole sentence forces the object into the partitive case. If the sentence were positive, the object would be the total object: Meillä on varaa tehdä pitkä ulkomaanmatka.

English says to "take" a trip. Why does this sentence use tehdä (to do/make)?

In Finnish, you "make" a trip (tehdä matka) rather than "take" one. Using ottaa (to take) here would imply physically grabbing something, which sounds unnatural in this context.

What case is being used in the time expression tänä vuonna?