Yup, no WAGS about it. In order to keep a mission running they need: people to design science sequences, people to translate those sequences into spacecraftese, uplink time on the Deep Space Network to send the instructions to the spacecraft, downlink time on DSN to receive the data, and then they may or may not be paying people to analyze the data, and that’s no small potatoes.
However, I don’t think (I may be wrong) that the DSN time is not paid out of the project budget. NASA runs DSN, and it may have its own operating budget that’s independent of individual missions. Spacecraft missions may just have to propose for uplink and downlink time. (They definitely do radio astronomy with the DSN, too, and like almost every other telescope, it’s free to use if your proposal is accepted.)