Dex, just had a quick look but didn't find the value of the cash economy. Thou I would say that a credible estimate would be difficalt to come up with.
I'm sure it's not that much, sure people only pocket the odd $50 or so
Anyway, while government misses out on some tax this cash money feeds the economy. Having a bit of cash allows for that occasional night out or the like that you may not have done.
Oh just remembered I have near $4000 cash in the unlocked car glove box, will bank it tomorrow