I don't know anything about prices, but if someone wanted to display one of those in the house, a parking meter would make a cool piggy bank!
Just have plenty of nickles and dimes to make change for quarters, dollars etc...
And if they don't hold a lot of coins, mom and pop could periodically empty and replace with paper money or just a paper saying how much the kid has saved up for the day when it's time to 'count' the money.
Or let the kid do the counting each time...or have the kid keep track of his 'time' earned, like maybe time at an amusment park etc.