Struggling to Formula Fields

Struggling to Formula Fields

Hello! 
I'm trying to create a Formula Field in the Product area. My intent is to create a Secondary Unit Price that may have a different value from Primary Unit Price if Unit Usage is "CPM" (cost per 1000).

Here is what I want:
if Usage Unit is CPM then divide Unit Price by 1000, else keep Unit price as it is (Unit price * 1)
Here is my formula:
If(${Products.Usage Unit}=='CPM',${Products.Unit Price}*0.001,${Products.Unit Price}*1)

And here is the error message I get:
  Your string is either missing its quote marks, or it needs a comma separating it from another value.

Any help will be very appreciated!

Cheers!

M