What did a medieval knight earn?
24 pennies a day at war, twelve times a farm hand's.
About $8,800 a month in today's gold.
A month of that pay weighs about as much as 3 AA batteries in gold.
Wages are pocket money. The real prize is a captured Frenchman worth a ransom.
Where the money came from
Knights stood at the top of the gentry, landed families below the lords who bore coats of arms, ruled over their tenants and helped run the shires. The crown held that every man with more than £40 a year from land ought to be a knight, and at times tried to force such men to take it. In the first half of Edward III's reign there were about 1,500 knights, or men rich enough to be one. At war a knight was paid 2 shillings a day, twice an ordinary man-at-arms and half a banneret, an officer with his own oblong banner. In 1350 the farm labourers at Yalding got 2 pence a day, so a knight earned twelve times as much. Wages alone drew few volunteers: in the unpopular campaign in the Low Countries from 1338 to 1340, the horsemen had to be paid double. Parliament paid better: every county sent two knights of the shire, and each could claim 4 shillings a day in expenses while away from home, twice his pay at war. The real lure was ransom and plunder. John Coupland, an obscure squire from Northumberland, captured the Scottish king, David II, after the battle of Neville's Cross in 1346. Edward III made him a knight banneret and gave him £500 a year for life, twelve and a half times the £40 that made a man a knight.
Sources: erenow.org · erenow.org 2 · themcs.org · en.wikipedia.org
What a knight's pay bought in 1350
a plough: less than a day's pay
an ox: a week's pay
a year's food for one adult: 3 weeks' pay
a great stained-glass window: 19 months' pay, more than a whole year of it
a warhorse: 2 years' pay, more than a whole year of it
Every price of 1350, with its source, is on the prices page.