Newegg offers the P3 International Kill-a-Watt Electricity Usage Monitor, model no. P4400, for $18.99. Coupon code "EMCWPHB85" cuts it to $15.99. With $2.99 for shipping, that's the lowest total price we could find by $1, although we saw it for $3 less in February. This usage monitor connects to appliances to calculate their electricity expenses by the day, week, month, or year.