Drones do not need Riggers to operate, they can be operated remotely by someone with a computer/commlink/cyberdeck and appropriate access permission (or a hacker who breaks in). Drones can also be independently operating, with PilotSoft programs controlling the whole thing. A Rigger’s special augmentations and training just make them a hell of a lot better than any of these other options.
By way of comparison: just about anyone with a grill can make a burger (standard user operating the drone) and you can also buy a premade microwaveable burger (software controlled drone), but Gordon Ramsay’s (the rigger) going to cook a way nicer burger than anyone else.
Anyhow, since it sounds like you’re going to be building this as an NPC enemy... You don’t actually need to worry much about the specifics. Come up with a set of stats that work for you and throw some dice.