Amazon.com has Thames & Kosmos Physics Workshop on for $18.92

• Kit includes more than 300 building pieces
• Build a windmill, two-speed crane, force scale, sail car, mars robot, hammer machine
• Experiment with simple machines: gears, levers, screws, inclined planes, pulleys, wheels and axles
• Learn and understand the most fundamental physics equations
  It is a 64-page, full-color experiment manual
• Centrifuge, pinball game, centrifugal switch, ship’s lantern, and dozens of other models