What about simply reduce the price of AV / AP mines ? Make the price of AV / AP mines depend on local population : 50/75 if you're not underpopulated, 25/37 if enemy are 50% more than you, 0/0 if enemy are 100% more than you (maximum). For the calculation, it take into account the territorry you're in but also the territory that are adjacent by lattice connection.
I dont think Ive ever run out of nanites since they reduced their recharge time, are you just chucking the mines on the ground in the spawnroom then restocking?