Amazon offers its Prime members Think Fun Math Dice
with free shipping
. (Non-members can spend $25 or more to qualify for free shipping; otherwise, shipping costs $4.07.) That's the lowest total price we could find by $3. This game purports to teach mental math skills.
Also available is Think Fun Math Dice Jr. for $4.99 with free shipping for Amazon Prime members. That's another price low, by $4.