So you say there was a stock or financial instrument (let's forget silly currencies for now) for which $1.00 (plus commission) would buy a US billion of them (see note).

I am pretty sure (from past software experience with SEC and major banks) that there is a limit to the number of decimal places allowed for a stock's price - and I think it is 4 d.p.

A simple Google search ("lowest stock price ever traded") was not immediately of help. What search string did you use?

Why not just save the Internet bandwidth and tell us one of the instruments thus priced!

NOTE

When I was but a child, the meaning of 'billion' was 1,000x more in Europe than in the U.S. - which I discovered when I moved to the USA. A UK billion was (many people still think it is...) one million million, i.e. 1,000x a US billion - much kinder on the nerves when discussing a national debts in Europe....

http://en.wikipedia.org/wiki/Long_and_short_scales