It could be scaled down to the size of a normal minigun, but even that is about $50 per second.
Meanwhile drone costs keep falling, Ukraine is well below $500 per drone now.
Also, I don't think you need 30 mm bullets to take out a drone. Those bullets are for much more hardened targets.
Modern CIWS will use radar to track their own outbound bullets and adjust their aim in real time to hit the target.
It could be scaled down to the size of a normal minigun, but even that is about $50 per second.
Meanwhile drone costs keep falling, Ukraine is well below $500 per drone now.