Walmart offers the The Dangerous Book: Essential Electronics Science Experiment Kit for $20.65. (Tom's Toys via Amazon offers it for the same with free shipping for Prime members.) Opt for in-store pickup to avoid the $5.97 shipping charge. That's tied with our mention from a week ago and the lowest price we could find by $16. It allows children to experiment with circuitry, resistors, capacitors, diodes, LEDs, and static electricity by building an electromagnet, electric motor, voltaic pile, joy buzzer, and a vibrating bug.