Hmm, there have been times where there have been ridiculous amounts of food selling at 4.
So really, if you just lay low while prices are high and just focus on research, getting ships, getting planets with high land count, and increase loyalty on such planets, then once food prices hit rock bottom you can pounce and buy the food for cheap.
All there is to it. Cuz see, if food is high now, folks are going to have an incentive to go agriculture and you can bet there are a lot of empires in np just setting up for an uber agriculture empire setup.
So go counter and do the counter-intuitive thing and go tax while food is high. You don`t have to actually have a high pop until conditions are more favorable.