We describe the construction and operation of three low-cost schlieren imaging systems that can be fabricated using surplus optics and 80/20, an aluminium extrusion based construction system. Each system has a different optical configuration. The low cost and ease of construction makes these systems highly suitable for high-school and undergraduate laboratories. Undergraduate students responded enthusiastically to the experience of assembling and operating these systems. This experience also served as an introduction to issues in optical design, helping the students gain an intuition for geometrical optics.