Setting aside the cost, it will take a long time to build that bridge.
Literal
Costs [topic-は] aside [as for-として], that bridge [object-を] build [for-には] long time [subject-が] take [probably-だろう].
Uses は別として ('setting aside') to bracket the cost issue and focus on time. 架ける ('to span, build a bridge') is specific to bridges, while the more general 築く means 'to build/construct.' Both are valid for bridge-building contexts.