"They are cheap in the evening."
Translation:Ei sunt ieftini seara.
It is expressed by the definite article (-a): seara = in the evening, iarna = in the winter etc. There are comparable expressions in English, such as "the other day."
Is "Ele sunt ieftine seara // sunt ieftine seara" incorrect? Because I tried and it didn't work, and on wikipedia it says "ieftin m, n (feminine singular ieftină, masculine plural ieftini, feminine and neuter plural ieftine)"