People have no idea how efficient farming is. In 1260 the price of wheat was 6- 8 shillings (~1/3 pound sterling) per bushel (60 pounds). By the early 20th century, it was about 1 £/bushel. At that point the US became the efficient grower and dominant currency, and so switching from pounds sterling to dollars at the rate at the time of $5/£1 is appropriate. Today wheat is $6.50 per barrel. Put another way, the price of wheat in the dominant currency has ~tripled in 750 years. That's an inflation rate of ~0.1%.

Put another way, a typical Saskatchewan dryland wheat farm is about 5,000 - 10,000 acres per employee or operator in size. That 5,000-10,000 acres will produce enough calories to feed ~100,000 people. (Those acres will also require ~$10M in capital and ~$1M in annual operating expenses)

Put a third way, modern agriculture can provide enough grains and legumes to feed somebody for around 30 cents per day at bulk prices.