Complex sentence: The 21st century has seen a resurgence in rickshaws, this time in auto rickshaws, also called velotaxis, because they are about 1/3 to 1/2 the cost of regular taxis.
Split into simpler sentences: The 21st century has seen a resurgence in rickshaws, particularly in motorized rickshaws and cycle rickshaws. Auto rickshaws, also called velotaxis, have resurged as they are about 1/3 to 1/2 the cost of regular taxis.