What did a medieval duchess earn?
5,000 marks a year: about 3,333 pounds.
About $730,000 a month in today's gold.
A month of that pay weighs about as much as 6 litres of water in gold.
The king's mother, on five thousand marks a year, and still complaining about the rents.
Where the money came from
On 1 June 1461 Edward IV gave his mother, Cecily Neville, a bundle of estates and customs money meant to bring her 5,000 marks a year; a mark was two-thirds of a pound. The estates were hers for life only. She held land in nineteen counties, from the castle and town of Stamford to an inn called the George in Grantham, and Clare Castle in Suffolk was part of the same grant. Her bailiffs, the officers who ran each manor, collected the rents. At Grantham one man rented the south mills from her for more than £6, and the George was leased for more than £13. A few old rents were still owed in kind: one Stamford shopkeeper paid her a pound of cumin, though most such rents had turned into cash, like the 2 pence one tenant paid instead of two barbed arrows. Her bailiff at Grantham, Henry Courteys, was also the town's alderman, its elected head, and he got 26 shillings and 8 pence a year from her. In 1459, when her husband's lands were seized, she had won only £600 a year to keep herself and her children. Her 5,000 marks were more than five times that, and 2,500 times her bailiff's fee.
Sources: richardiii.net · en.wikipedia.org · en.wikipedia.org 2 · en.wikipedia.org 3
What a duchess's pay bought in 1350
a year's food for one adult: less than a day's pay
a great stained-glass window: a week's pay
a warhorse: a week's pay
Harlech Castle: 3 years' pay, more than a whole year of it
the ransom of the King of France: 170 years' pay, more than a whole year of it
Every price of 1350, with its source, is on the prices page.