Cheapest Air Pillows — Pre-Inflated Void Fill
Air pillows are the modern alternative to packing peanuts — lighter, cleaner, and faster to pack. Pre-inflated pillows arrive ready to drop into boxes. Deflated film rolls require an air-pillow machine ($200-400) but cost 80% less per pillow at scale. For sellers shipping 10+ packages per day, film rolls are dramatically cheaper. For occasional shippers, pre-inflated bags are easier.
Current listings — sorted by price

4x8 Air Pillows Inflatable 330 Count Void Fill Package Dunnage - Includes Pump

2 PACK 1000ft x16" Air Cushion Machine Film Bubble Pillow Packaging Padding Roll

AirPillows™ 150 Count Premium Void Fill Package Shipping Air Cushion Padding

4'x 8' Air Pillow, Color Blue, total 3 packs
Buying tips
Pre-inflated pillows cost $0.04-0.08 each. Deflated film (requires machine) drops to $0.01-0.02 each. Break-even on the machine is around 5,000 pillows.
Standard size is 4×8 inches. Two pillows fill the top of a medium box; 4-6 fill a large box. Order based on your average box size, not your item count.
Air pillows are lighter than peanuts (reduces DIM weight impact) and don't shift during transit — they wedge against the item and hold position.
Pop and recycle after use. Unlike polystyrene peanuts, deflated air pillows are flat plastic film that goes in standard recycling.