I'd start with a toy cash register which includes play money and credit cards (although the latter are of dubious value to a child). We always had a grocery set with a cash register, a pretend scanner, toy food and so on. Grocery stores are the places most kids are familiar with. You can buy extra play money (bills and coins) in any toy store. You can make up prices now and later on you can start with basic addition (don't do that now). You can also save some of your boxes from the recycling bin (cereal and pasta boxes, for example).
Playing board games with money is also fun. Monopoly is too much now, but look for some junior versions of games.
You can also use the "pizza" method that teachers use for different things. Make a "pizza" out of sturdy card stock and draw a $1 symbol in it. Make some additional wedges with 25 cents on them and a picture of a quarter. 4 quarter sized wedges can be laid on the main pizza cutout, and still make a whole pizza and therefore a whole dollar. You can do the same with a pizza cut into 10 slices for dimes, and a child can mix/match 5 dimes and 2 quarters to still make a whole $1 "pizza." You could also use craft foam or have the card stock laminated at any print shop. I'd use different colors for the different size wedges. You could make several sets and then the child could have, say, $2.50 with 2 whole pizzas and 2 quarter wedges. Then build from them with $10 bills or $20 bills as he gets better with more numbers.
I used this method to teach music - a whole pizza = a whole note, 2 halves = 2 half notes, quarter notes and 8th notes, same thing. Kids learned that if a measure of music had 4 beats, there were multiple ways to make up that 4 beats (4 quarter notes, a half & 2 quarters, 8 8th notes, a half and a quarter and 2 8th notes, etc.). That also reinforced fractions that they learned in their math class.
If you recycle your bottles, have your child help with that at the redemption center. I know it's a pain and usually I just curb recycle mine, but when my son was younger, he was in charge of that. He thought $1.25 was a huge deal, you know? If the machine gives change, you can help him exchange that for quarters and dollars.