You just about nailed it. Just needed some zeroes and a special case to handle the value of zero as being dollars; not percent.
Here's what I ended up using:
[=0]$#.00;[<=100]#.00"%";$#.00
Thanks a bunch folks!
That's a brilliant formula but I can't use a formula in this instance.
The cell that gets typed into needs to interpret and display the correct format; that's why I was trying Custom Formats or Conditional Formatting since they affect the format of the cell that holds the typed-in value...
This one is challenging.
I want a cell to be formatted as % if value <=100 and as currency if >100. [The context changes that if data is 100 or less, it needs to be treated as a percent; any other value should be treated as a real number.]
I tried using the following custom format...