Even "$500k/yr" is an improvement on "$500k p.a.".
Did you notice that a fluent English speaker had to ask what "p.a." meant? Do you think that would have happened if it had been written "per year" instead?
Because p.a. is also part of my language.
These are Latin phrases, borrowed especially in British English as Great Britain was occupied by Latin speakers for nearly 400 years -- 43 CE through 410 CE. Latin continued to be the language of diplomacy, religion, philosophy, and science through the 18th and 19th century.
It is, for all practical intents, proper British English.
Though yes, $<value>/yr. is more frequently seen especially in American English.
Can you explain how Latin loanwords were loaned into English during this period? In your explanation, please make use of the facts that (1) there were no English speakers in Great Britain before 410 CE, and moreover (2) there was, by definition, no such language as English until Anglo-Saxon migrations into Great Britain (around 450 CE) established a distinct West Germanic linguistic community on the island.
You are, otherwise, being what the modern English derivative of the Sumerian ansu describes.