National Equipment Parts via Amazon offers the Aprilaire 700 Automatic Humidifier for $191.19 with free shipping. That's the lowest total price we could find by $18. Features include service, temperature, and relative-humidity indicators and a range of up to 4,200 square feet.
Target offers the Holmes Arm & Hammer Humidifier Demineralization Tablet 4-Pack for $4.48. (Amazon has it for the same price with free shipping for Prime members when you spend $25 or more.) Opt for in-store pickup to avoid the $4 shipping charge. That's the lowest total price we could find by $6. They're for use in Holmes humidifiers.
Walmart offers the Crane Ultrasonic 1-Gallon Cool Mist Humidifier in Duck or Gator for $26. (Amazon charges the same with free shipping for Prime members only.) Opt for site-to-store pickup to dodge the $4.97 shipping fee. That's tied with our February mention as the lowest price we've seen. (It's the best now by $5.) It features a run time of up to 24 hours, auto-off function, and 1-gallon tank.