With orders of $25 or more, Amazon offers Prime members the Bell Toddler Frozen Helmet in 3D Tiara for $4.85 with free shipping. (Non-members can spend $49 to bag free shipping.) That's the lowest total price we could find by $25. It features reflectors for visibility and fits head sizes 48cm to 52cm.

Note that this item is part of Amazon's "Add-on program" and can only be purchased with an order of $25 or more.