So the farmer just needs money? He has no maintenance costs? He doesn't like to watch movies? He's just going to sell his food, and put all the money gained thereby into the bank, where it sits, doing nothing, right? Yeah, no, It doesn't work that way. He has costs, too, and desires. The money he gets from selling his food will go to pay for those needs, expenses, and desires. That puts the money back out into the market.
No the farm owner doesn't really need money, even though he'll be offered plenty of it; he controls the goods that money is worth anything for, and only 24 hours in a day to enjoy its worth. He might have a use for 50 million people, and gives them grain for their services via money, but if he can feed the total 100 million that exist, what are the other 50 million people to do to get the food he controls?
The farmer typically doesn't give a shit who eats his food. All he cares about is that someone buys it. Thus, he seeks the money for the food, and uses that money to buy services and (here's my next point) other consumer goods. Food is not the only consumer good out there, it's just one of the few that
everyone needs. He's also not the only farmer, nor does he supply the only type of food.
But let's assume that there is one farmer supplying all the food to everybody. He has enough food for all 100 million people. The people all have enough money to buy the food. They do. Now he has a great deal of money, but, say, only enough food to feed himself. What now? Well, now, he takes that money and buys a TV, a new couch, some booze (likely made from his grain), some fertilizer, new farm equipment, watches movies, gets a blowjob, etc, until he's out of money. By that time, the crops are in, and he has food again, and no money. The people have eaten all their food, and by virtue of providing services and other consumer goods to the farmer (and each other), the people have money. The cycle starts again.