It's not a new concept. Depending on how you distribute your inherently expensive guidance systems, you can either make a system very expensive, or not so expensive.I’m trying hard to reconcile a concept that offers a “cheap” round with precision guidance.
It also depends on questions like "Do we want it to be guided and corrected the whole path, or can we settle for maybe 50% of the path down to terminal stage? Or can we go down to terminal stage only?"
For example, INS guidance can be extremely expensive if the guidance system works the entire flight and the flight itself is very long. IIRC a Peacekeeper ICBM's INS cost about $300,000 in 1989 dollars,
The Peacemaker missile's navigation suite featured the most precise and complex self-contained gyro system ever built. It had 19,000 individual parts.
But if you take an INS and couple it with, say, a GPS that recalibrates it mid-flight, then the INS itself needs to be exponentially less complex and expensive.
"Active" forms of guidance can be expensive, but some are cheaper than others.
A long range projectile like that should not have expensive guidance equipment. In fact, it could do entirely without any active form of guidance, even optical sensors (yeah I know they're technically passive).
A GPS receiver and a recalibrating INS should be, in military terms, dirt cheap.
The most expensive components should actually be the propulsion, and as in the case of the $1 million HVP, a major cost factor is development costs which simply were not divided between ordered units.
As for why a gun is desired over any other solution, is beyond me.