For Prime members only, Amazon offers the Summer Infant Double Safety Bedrail in Grey, model no. 12554, for $25 with free shipping. That's the lowest total price we could find by $6, although some stores charge around $50 or more. Each panel measures 42.5" x 21" and accommodates twin- to queen-sized mattresses and platform beds.
Note: It's expected to ship within one to two months.