which is correct?

a couple billions of dollar

or

a couple billion of dollars

3 answers

Neither --

"two billion dollars" would work just fine and is less iffy.

Commonly understood:
a couple = 2
a few = 3 to 5
several = 5 or more

And when you use "a couple" in a sentence like this, you need to add the word "of" after it: e.g., I have a couple of CDs I'd like to get rid of.
then would "it cost them billions of dollars" work?
i just don't know is the -s on billion or dollar.
Yes, you could say any of these:

It cost them billions of dollars. (Make sure it's clear what "it" is.)

It cost them two billion dollars.

It cost them a couple of billion dollars. (This is not as formal as the other two, however.)

What is your choice?

=)