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Amazon [amazon.com] has 6-Pack Filtrete 23.5×23.5×1 AC Furnace Air Filter, MERV 11, MPR 1000, Micro Allergen Defense, 3-Month Pleated 1-Inch Electrostatic Air Cleaning Filter for $24.85 – 5% when you check out via Subscribe & Save = $23.61.
Shipping is free with Prime or on $35+ orders.

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5%: $23.61
10%: $22.36
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