What did a medieval king earn?
About 100,000 pounds a year, mostly customs duties on wool.
About $24 million a month in today's gold.
A month of that pay weighs about as much as 3 washing machines in gold.
Over two tonnes of gold a year, and Edward III still pawned his crown to pay for a war.
Where the money came from
A king drew no wage: he lived on his lands and on what his subjects paid him. Edward III had a steady income from the crown lands and could borrow large sums from Italian and English lenders, but war needed far more. Parliament could grant a tax on movable goods, usually a tenth in the towns and a fifteenth on farmland, but each one had to be asked for and its need proved. The steadiest money came from wool shipped abroad. Every merchant paid 6 shillings and 8 pence on each sack, and in wartime a heavier tax was laid on top, nicknamed the maltolt, 'the bad tax'. For twenty years from the early 1340s it stood at £2 a sack, six times the old duty, and from 1362 parliament let him keep collecting it even in peacetime, at £1 a sack. From 1353 to 1362 the customs brought in on average £87,500 a year, over six times the average of his first ten years, and in 1359 they let him lay out about £75,000 to invade France without asking parliament for a tax. Even so the money ran out: in February 1339 he pawned the Great Crown of England to the Archbishop of Trier, promising to repay £16,650. Over the twenty-five years from 1351 the customs brought him about £1,750,000, more than all the direct taxes of his whole reign.
Sources: en.wikipedia.org · erenow.org · erenow.org 2
What a king's pay bought in 1350
a great stained-glass window: less than a day's pay
a warhorse: less than a day's pay
Harlech Castle: a month's pay
the ransom of the King of France: 5 years' pay, more than a whole year of it
Every price of 1350, with its source, is on the prices page.