Hi Angliholic
Are you sure 'grand
s' was used and not 'grand'?
Saying 'two grand' to mean 'two thousand dollars' would be a typical usage. Adding 's' to 'grand' would normally sound odd to my ear. However, the addition of "One for you and one for me" does help justify it.
I'd say the addition of 'of green' is a whimsical addition to the usual expression, and 'green' refers to 'greenbacks'.
(OT: I wonder how long the word 'greenback' is going to survive seeing as US bills now come in a variety of colors.)