I'm looking for offers around 80% of the military value of each country. If no offer satisfy me, I will most likely sell the weapons on the market and directly and try selling the countries again, with their population and stockpiles intact.
These countries have some surprises worth considering. For instance, Perseus Army still has supply units with one weapon, Outer Army has 381 018 087 units of ammunition quality upgrades and Milky Way has 50T in its investment fund.