As regards cut price defensive and offensive weapon systems. a few weird and wonderful WWII ideas should be operational now!!
Balloon Barrage. Took out a few V-1's in 1944. With modern electronics could come with small proximity fuzed warheads up the line (fibre optical line would allow remote arming / disarming), plus lightweight carbon fibre / nylon lines would allow stuff that goes bang to be strung between balloons.
Operation Outbound. Royal Navy balloon bombing campaign against German electrical grid and rail electrical system. Balloons dragged wire over power lines causing Phase shorts between the lines or the ground with shorted out the power systems causing trips of Substation breakers and damage to transformers . US did the same against Iraq gird with wire chucking Cruise Missiles in 1991. Use drones.
Parachute and cable system. Rockets today can be fitted with very cheap guidance systems that will allow them to fly in a direction you want and deal with any off axis disturbance. Build a device that will fire 5 rockets at the same time in a 120 degree arc from a central location with carefully packed lightweight cables in between them out to a distance of 200 metres of so with the device hidden on a hedge line as a Russian Helicopter just about to fly over it at low level. Attach some warheads to the rockets and cables bottoms. Warhead self destruct after 30 seconds or so if the lines don't wrap around the chopper and drag a bomb on to it. Would have a faster reaction time than a MANPADS.