Ace Hardware offers the Rayovac 9-volt Alkaline Battery 8-Pack
for $15.99. Opt for free in-store pickup to dodge the $9.39 shipping fee. At $2/battery, that's the lowest total price we could find for this quantity by $3. Sales tax is added where applicable. Besides powering devices that require 9-volt batteries, these cells are notable because our dad would often touch them to his tongue to see if they had any charge left.
Update: As a reader found, Amazon offers it for $13.33 with free shipping via Subscribe & Save.