Cheap telemetry overlay chip for rov


I am currently building an underwater ROV. The rov is controlled via serial from the remote on the surface and has a composite video signal from the onboard camera, this feeds a small 7inch monitor mounted on the remote. I am planning to use the telemetry data that is sent to surface from the rov via serial to be used as an image overlay. I need to know what is a cheap way of injecting the text into the video signal from either another arduino (acting as the bridge from serial to ) or direct uart serial. What are my options?

Maybe something like this