Setting aside the cost, that construction will probably take quite some time.
Literal
Costs [topic-は] [setting aside-さておき] that construction [for-には] considerable time [subject-が] take [probably-だろう].
さておき means 'setting aside, leaving aside' — a slightly more casual equivalent of は別として for bracketing one topic to focus on another. The sentence reserves cost discussion and directs attention to the time required for construction.