Feb 23rd 2014, 12:03:22
When your ($$ upkeep expenses + food upkeep expenses of 1 turn) / (NW gained from 1 turn of production) is higher than $262/NW, which is the average price of your private market. You won't reach this unless your NW is over 150m-200m, depending on your land size.
Explanation: You have $X money on hand which is 1 turn's worth of upkeep. You can either spend X to buy from your private market, or use it to pay for expenses for 1 turn and run 1 turn. If the NW gained from running 1 turn is higher than spending the same amount on private market, you do exactly that.
This obviously assumes the public market is more expensive (which is going to be always true at the end of a reset, particularly with 10% commission). You may use $240/NW as the threshold if you have very little cash and can only buyout troops and tanks. Note you can almost always sell to public above $266/NW (after commission it will be ~240/NW) and use that resulting cash to clear your PM (or run turns whichever is cheaper). This is called reselling.
