This paper presents the design, implementation, and validation of a prototype based on an ESP32 microcontroller and a PZEM-004T module for measuring electrical variables (voltage, current, active power, power factor, frequency, and energy). Data are transmitted every 20 s via the MQTT protocol to the U0bidots platform, where they are stored and processed to compute bimonthly consumption and estimated billing cost. The system was tested in a residential environment over three consecutive bimonthly periods, achieving an average error below 0.67% when comparing the estimated cost calculation with the invoice issued by the utility provider. The prototype demonstrates the feasibility of a reliable home energy monitoring solution with integrated real-time cost analysis.