Walmart offers the Sand N Play Build A Box, model no. 3028-05, for $39.01. Opt for in-store pickup to dodge the $5.97 shipping fee. That's the lowest price we could find by $8. The modular locking pieces feature a canal for water and hold up to 200 pounds of sand. It comes with a water-resistant fabric cover that doubles as a carry bag.
A close price: Target has it for $39.99 with free shipping.