From A Day by Day Chronology of Mr. Sherlock Holmes according to Zeisler and Christ by William S Dorn:
On May 19, 1900, Lord Saltire was rescued. [PRIO]
[Holmes said,] “I will help you, but on one condition only. It is that you ring for the footman and let me give such orders as I like.”
Without a word the Duke pressed the electric bell. A servant entered.
“You will be glad to hear,” said Holmes, “that your young master is found. It is the Duke’s desire that the carriage shall go at once to the Fighting Cock Inn to bring Lord Saltire home.”
Also on May 19, 1900, the Duke of Holdernesse wrote a cheque for £12,000 to Holmes. [PRIO]
The Duke took a pen in his quivering fingers and opened his cheque-book.”I shall be as good as my word, Mr. Holmes. I am about to write your cheque, however unwelcome the information which you have gained may be to me. When the offer was first made I little thought the turn which events might take. But you and your friend are men of discretion, Mr. Holmes?”
According to Nicolas Utechin’s Coin of the Canonical Realm, in 2013, that £12,000 would have been worth approximately £1,065,600 GBP ($1,715,616 USD). Small wonder Holmes said that cheque was the most interesting thing he had seen in the North!