I'd never come across the term 'payday loan' before seeing this article. It's a loan designed to tide you over till payday (I've always known that as a sub or advance). It was the name of the company offering such loans (which carry an astronomical interest rate) that caught my attention - Wonga.
Wonga is mainly a British English slang word for money. The OED's first citation is dated 1984, but the word itself is much older. It was used by gypsies or Romany (or Romani) travellers in Britain in the 19th century with the meaning 'coal' (when it was spelled wongar or vongar). Coal may have been slang for money at the time. Indeed there is an entry 'to post the cole' in the OED, which is defined as 'to pay down the money'. That phrase dates back to the 17th century.
Wonga is more likely to be used in an ironic sense, or in tabloid news reports. For instance, the Sun has nicknamed Stephen Hester, the chief executive of the Royal Bank of Scotland, Stevie Wonga, and the headline of an article in the same newspaper is the alliterative "Strictly waltzes off with Wossy's Wonga" (note for those who don't read The Sun -- Strictly is short for the BBC TV programme Strictly Come Dancing and Wossy is the nickname of Jonathan Ross, formerly a very highly paid BBC celebrity who has just left the Corporation).