The cost of a garbage bag full of aluminum cans can vary depending on the scrap price per lb of the aluminum cans.
At the scrap yard here they're giving 30 cents per lb for scrap aluminum cans and I took in 3 bags a few days ago and got a whopping $9.00 out of the cans.
I don't do it for the money but I save the cans that I do drink soda out of and it pays for a bit of gasoline on my way to work.
You can make lots of money if you have enough aluminum cans to sell but just out of one bag it's not usually worth it to take it to scrap yard unless you're going that way anyway.
So I'm estimating I got paid around $2.50 cents per bag of aluminum cans.
It's better than it going to the dump though and I get a little gasoline money.