For Prime members only, Amazon offers the SwimWays Star Wars Death Star XXL Light-Up Beach Ball for $9.09 with free shipping. (Toys"R"Us charges the same with in-store pickup.) That's the lowest price we could find by $11. It measures 31" and features LED lights.

Update: The Amazon offer has increased in price; however, Toys"R"Us still has it for $9.09 with in-store pickup.