ESRGAN (Enhanced Super-Resolution Generative Adversarial Networks) is a free and open source video enhancer. The code and the trained model that it uses are available to the public on the ESRGAN's GitHub repository.
This means that you can download and use the model for free and even modify it to suit your specific needs. However, keep in mind that the usage of ESRGAN may require some technical expertise and computational resources like GPU.