Amazon[amazon.com] has 3-Count Energizer 357/303 Battery Pack for $2.37 when you 'clip' the $2 off coupon on the product page and checkout via Subscribe & Save. Shipping is free.
Note, you may cancel Subscribe & Save anytime after your order ships. Select the later date from the "First Delivery On" menu to get traditional S&S checkout instead of adding to your cart. Eligible Amazon Prime members may also qualify for a $1 No Rush Shipping credit valid toward the future purchase of select digital eBooks, music, movies, or TV Shows via Amazon (more info[amazon.com]).