With orders of $25 or more, Amazon offers Prime members the
Meguiar's M10 8-oz. Mirror Glaze Clear Plastic Polish for
$1.98 with
free shipping. (Non-members can spend $35 to bag
free shipping.) That's the lowest total price we could find by $3. It's designed to restore optic clarity to clear plastics.
Also with orders of $25 or more, Amazon offers Prime members the Meguiar's M17 8-oz. Mirror Glaze Clear Plastic Cleaner for $2.58 with free shipping. That's the lowest total price we could find by a buck. It's designed to remove hairline scratches from clear plastic.
Note that both items are part of Amazon's "Add-on program" and can only be purchased with an order of $25 or more.