Walmart offers the Duck Brand Shrink Film Indoor Window Kit 10-Pack for $10.94. Opt for in-store pickup to avoid the $5.99 shipping charge. That's the lowest price we could find by $2, excluding the below mention. (For further comparison, we saw a 5-pack for $4 in July, although that required a $25 purchase.) The kit includes two films and two rolls of tape, which is enough material to cover and insulate up to 10 3x5-foot windows.

A close price: Bargain Buy Quest via eBay offers it for $11.59 with free shipping.