Basically Glacier Girl is a new build aircraft that used some existing components.
There’s no way that you could get the price of a comparable military aircraft down to $1 million. I’d think the $10 million for GG is the floor, cost-wise. Once you start adding in required MilSpec hardware (comms, jamming, targeting, bang seat) and adopt a contemporary powerplant (not going to put Allisons or Merlins back into production) the price is really going to spike. To the point where it would just make sense to keep the A-10s with all their wonderful sunk costs (esp for the ones that were just rewinged) around for another 30 years.
Maybe, but there is actually a program for a Low Cost Battlefield Attack Aircraft (LCBAA) with the target price of no more than $1,000,0000.
The goal is to make thousands and strip out most everything.