Brewer's Dictionary of Phrase and Fable suggests that quid might not come from the Latin for what, but it first appeared in print as early as 1688.
Cassell's Dictionary of Slang suggests that sheet for both � & $ is short for a sheet of paper.
Like all these slang terms their origins are open to debate.
Hope that helps you a little.
Yep, back in good old days when you could do your weekly shopping for 10 bob a pound note was rarity and the often the only paper money a person would have.
It was called a sheet - it was a big sheet of paper compared to today's fiver.
The Shorter Oxford English Dictionary gives:
" sheet: An American dollar bill; a pound note; the amount of a dollar or a pound sterling" and dates this use from the mid C20.
Wikipedia (OK, not exactly the most scholarly source in the world) says: ... possibly derived from the Royal mint at Quidhampton, Wiltshire, England, but more likely from the Latin phrase 'Quid Pro Quo' (This for that)meaning an exchange of goods...