Complex sentence: The RW19 was originally available as a complete kit, less only the engine, but today is only offered as plans and the designer estimates it will take 600 hours to complete the aircraft, although other estimates run from 300 to 1500 hours.
Split into simpler sentences: The RW19 was originally available as a complete kit, less only the engine, but today is only offered as plans. The designer estimates it will take 600 hours to complete the aircraft, although other estimates run from 300 to 1500 hours.