I think the ice cream man was my best teaching experience
:. We had a change jar in the kitchen that everyone could use. When we heard the music we would run around in a panic frenzy looking for any pair of shoes around (sometimes even my dads lol) and grab the jar. The ice cream man was oh so patient as we counted our coins on the sidewalk.
It isn't an every day type event of course but I still remember it 28 years later.
How about a garage sale and they can be the shop keeper with your help of course.
They can have fun putting price stickers or tags with a bingo marker color on items and then you could graph it to show them the prices.
We had a kool-aid stand and sold dixie cups of kool-aid for whatever anyone would give us. We kept raising our price but then would let kids have it for a penny.
You could have a good deed jar and use coins or paper money. When they do something..have them add their $ and then take them to the store to buy a prize. Or you could buy some little things and keep your own store in a box in your room.