Walmart offers the LEGO Duplo Number Train, model no 10558, for $14.99. (Amazon has it for the same price.) Opt for in-store pickup to avoid the $5.97 shipping fee. That's tied with our January mention and the lowest price we could find now by $12, outside of the stores below. This set comes with 31 pieces, including 10 numbered bricks.
Close prices: Target and Kmart each have it for $15.99 via in-store pickup.
Update: Kmart offers it for the same price.