Also should be accepted is: "The rent for this house is very expensive."

I think "very expensive" is a better translation than "so expensive"

This is a very badly translated question. It doesnt actually make sense ckearly in eather language do you mean the "ongkos untuk sewa rumah ini mahal sekali"

I am not a native speaker but we say "This house rent is very expensive."

In English the rent can not be expensive, it is either 'this houses rent is very high' or 'renting this house is very expensive'. The literal translation works in bahasa, but is an error in English.