Walmart discounts a selection of portable fans, with prices starting from $3.84. Choose in-store pickup to avoid the $5.99 shipping fee, or get free shipping on orders of $35 or more. (Some items may receive additional discounts for choosing pickup.) A couple of best bets:

Dreambaby Stroller Fan for $5.97 + pickup (low by $3)

Comfort Zone 18" HV Cradle Floor Fan for $36.92 + $0 s&h (pictured, low by $10)