Bach Bucks are a perfect motivator for children because they get paid to practice without really being paid.  I have some prize boxes filled with $5 items, $10 items, and so forth (the real cost of these prizes are all mostly under $1.)  If a child practices at least 5 times in a week she can earn a prize every week, but she may have her eye on a more expensive or bigger prize and save her bach bucks.  I also have cans of soda pop and candy bars in a $30 prize box.  They're not expensive for me to buy, but the kids LOVE to save up for them.