Electromagnetic waves propagating through the Earth’s ionosphere are subjected to changes in group and phase velocities, refraction, dispersion, and diffraction. For systems relying on the usage of radio signals affected by the ionosphere, it is of crucial importance to account for these effects. As far as ionospheric monitoring is concerned, high-grade multi-frequency and multi-constellation Global Navigation Satellite System (GNSS) receivers are commonly used. The existing ground-based GNSS receiver networks can provide information on a global scale. Nevertheless, geographic regions still exist where ionospheric monitoring facilities are limited. To improve our knowledge about ionosphere in areas where the existing networks coverage is sparse, an increase in the receivers’ density would be desirable. The cost of the devices has indeed constituted a major obstacle, however, with the significant advance of software-defined radio, the situation is changing through the availability of low-cost solutions. The present work will discuss the performance of the available off-the-shelf low-cost dual-frequency GNSS receivers, testing them in the controlled environment and comparing the derived data with scientific-grade instruments. The accuracy of the collected ionospheric data, such as uncalibrated and calibrated total electron content (TEC) will be analyzed.