This is the 4799th most frequent Spanish word.
costosos
Expensive.
In this sentence, 'costosos' is used as an adjective to describe the products in terms of their high price.
Los productos en esa tienda son muy costosos.
The products in that store are very expensive.
Here, 'costoso' is used figuratively to denote the financial burden associated with maintaining a luxury car.
Resulta costoso mantener un auto de lujo.
It is costly to maintain a luxury car.
In this sentence, 'costosa' (feminine form) is used to describe the proposal in terms of potential costs related to time or money.